list use describe name differentiate identify - g · PDF filethe types of insects present. ... microorganisms work together to spoil food. Softening caused by enzymes can make it easier

18

406

Chapter 18Food Safety:Sources ofContamination

ObjectivesAfter studying this chapter, you will be able toidentify three main types of food contaminants.differentiate among the types of foodborneillnesses.name pathogens that cause foodborne illnesses.describe the two main ways pathogens enterthe food supply.use food handling procedures that will helpprevent the growth of illness-causingmicrobes.list the seven steps in developing a HACCPsystem.

Key Terms

A toddler is hospitalized as a result ofdrinking contaminated apple juice. A pre-schooler dies because he eats a hamburgerthat is not thoroughly cooked. A cruise shipcomes back to port early because many pass-engers have become ill with the same symp-toms. A school cafeteria is unable to operatebecause half the staff is out with symptoms ofvomiting, diarrhea, and fever. In each case,the illness or death was traced to something inthe food supply.

contaminationbiodegradablefood spoilagefoodborne illnesspathogentoxinfood intoxicationfood infectionsalmonellosis

parasitehosttrichinosisviruscapsidhepatitiscross-contaminationHACCP (Hazard

Analysis and CriticalControl Point)

USDA

Making regular sanitation checks of food processing equipment is a critical step in preventing contamination.

Chapter 18 Food Safety: Sources of Contamination 407

Types of Food ContaminationThe United States has the safest food sup-

ply in the world. Even with this record, somepeople get sick from eating food. Someexperts estimate up to half of all cold and flucases in this country may really be foodborneillnesses. People’s lives depend on a reliable,safe food supply that is free from harmful con-tamination. Contamination is the state ofbeing impure or unfit for use due to the intro-duction of unwholesome or undesirable ele-ments. Food can be contaminated by insects,rodents, chemicals, microbes, or other foreignparticles.

The addition of microbes is not necessarilybad. As you read in the last chapter, addingmicrobes to foods can result in many newfood products. You could say that bakedapples are contaminated if juice from a peachpie drips in from the rack above. Fortunately,the baked apples are still safe to eat unless youare allergic to peaches. However, the bakedapples are no longer pure. They have beencontaminated by, inoculated with, or mixedwith peach juice. This has made them impurebut not unfit or harmful.

In this chapter, you will study how andwhen harmful contamination occurs. You willfind out what steps you can take to help pre-vent it. You will also read about the differ-ences among contamination, spoilage, andfoodborne illness.

Contamination occurs when somethingnot normally found in the food is added.Contamination implies the addition is notintended or planned. The substance addedmay or may not cause problems. Three mainsources of contamination are from physical,chemical, and microbial sources.

Physical ContaminantsPhysical contaminants are substances that

become part of a food mixture. They may notchange or damage the food itself. However,their presence can create health hazards forthe consumer. For instance, metal filings orbroken pieces of glass have occasionally gotteninto foods. These materials would not spoilfood, but they could cause injury if swallowed.Other examples of physical contaminants

include packaging material, insects, androdent droppings.

Insect and rodent contamination presenttwo major problems. The first is the large vol-ume of food that insects or rodents can eatand/or destroy. It is estimated that as much as10% of the U.S. grain crop is destroyed annu-ally by insects. The second concern is themicrobes that may enter the food because ofthe insects or rodents. For example, flies pickup microbes on their hairy feet. When flieswalk on food, microbes can transfer from theflies’ feet to the food. Insects and rodents alsodamage the surfaces of foods such as fruitsand vegetables. This creates openings thatallow microbes to enter and multiply withinthe foods.

Insects and rodents can contaminate thefood supply at any stage of growth or produc-tion. For example, some insects lay eggs inwheat while it is growing in fields, 18-1. Theseeggs are not visible, and their presence insmall amounts is not harmful to humanhealth. Keeping all insect eggs out of thewheat supply would be extremely expensive.On the other hand, cockroaches are likely toenter the wheat supply during the processing

USDA

18-1 Aerial spraying of fields with pesticides pro-tects crops from insect and some microbial typesof damage.

This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

408 Unit V Food Microbiology: Living Organisms in Food

stage. Their presence is less acceptable andcan be affordably controlled by the food manufacturer.

The FDA examines food products forinsect parts. FDA inspectors want to identifythe types of insects present. To do this, theinspectors must be able to recognize insectsfrom fragments, such as antennae. Inspectorsalso need to know about the habits of insectsand the processes used to produce foods. Thishelps the inspectors determine the amount ofcontamination and the point at which the contamination occurred.

Chemical ContaminantsKeeping insects and other pests under

control can lead to chemical contamination.Insecticides are chemicals used to improve cropyields by reducing losses due to insects.Herbicides are used for the same reasons tocontrol weeds. Both types of substances arepesticides. If pesticide residues remain on food,they enter the food supply. The United StatesDepartment of Agriculture (USDA) monitorsall pesticides. Any substance used on cropsmust undergo thorough testing to see howeffective it is. Foods are examined forresidues. Tests are conducted to determinewhether residues pose a health hazard.

A second way chemical contaminants canenter the food supply is in water. Water is usedin the processing of nearly every food product.Water is an excellent solvent. Therefore, manypoisonous substances will dissolve in and pol-lute water supplies. The term toxic is used forsubstances that are harmful in low concentra-tions. Mercury, cadmium, lead, chloroform,benzene, and polychlorinatedbiphenyls(PCBs) are among the toxic substances thatmay get into water supplies.

Whether a substance is considered toxic ornutritious is often a matter of volume.Everyone needs very small amounts of zincfor good health. However, in high levels, zinccan lead to death. Too much of a good thingmay not be a good thing!

City and industrial water supplies areoften checked for toxic substances. However,there are no requirements for checking mostprivate well water sources. Homeowners areadvised to test well water routinely to protecttheir families from pollution.

Sources of Toxic SubstancesTwo main sources of toxins in water sup-

plies are pesticides and industrial waste. Theuse of some pesticides has been bannedbecause they are not biodegradable. Thismeans that, in time, biological systems willbreak them down into chemical parts thatnature can safely recycle. When pesticides donot break down, rain washes them intostreams and rivers. They travel on to lakes andoceans. In time, they can build up to toxic lev-els in the flesh of fish.

Pollutants from industry can enter thewater supply in a number of ways. Exhaustsemitted into the air can be carried to the earthby rain. Wastes may be dumped directly intobodies of water. Groundwater can filterthrough buried dump sites and carry pollu-tants into the water supply. Frequent testing offactory waste products and water sources isneeded to ensure the safety of the public.

One of the substances often dumped inindustrial waste is mercury. In the mid 1970s,the FDA warned consumers to stop eatingswordfish. The FDA was concerned about thehigh levels of mercury found in the flesh ofthe fish. Today, the tuna industry checks mer-cury levels as the tuna is packed. Standardsare updated as research reveals new informa-tion regarding toxins and their hazards.

Another case of a surprising pollutionsource occurred in 1998 in Crescent, Oregon.The city water supply was contaminatedwhen leaks formed in old, buried petroleumtanks. The tanks were from a bankrupt servicestation. Their removal was only 1 of 702approved underground tank cleanups forOregon in 1998. Building new subdivisionsover old gas stations, landfills, or industrialsites increases the chance of pollutants reach-ing underground water tables. This, in turn,increases the risk of contaminants getting intothe food supply.

LeadThe level of lead in the U.S. food supply

was 90% lower in 1992 than in 1980. Thisreduction was due to tighter FDA regulations,changes in gasoline, and voluntary changesfrom the food canning industry. A majorsource of lead was leaded gas, which createdexhaust that settled on crops and in water.


Another source of lead was the lead solderused to seal the seams on tin cans. The CanManufacturers Institute announced that, as ofNovember 1991, lead was no longer beingused to solder cans. Lead solder was responsi-ble for as much as 45% of the lead found infood before this time.

Consumers need to be aware of the otherways lead can leach into water. The mainsources are glazed ceramic dishes (includingchina), lead crystal glassware and decanters,and silver-plated hollowware, 18-2. The FDArecommends that you avoid storing acidicbeverages or foods in any of these containers.Heat and low pH increase the rate at whichlead leaches into water. This is why cups usedto serve hot, acidic coffee must meet thetoughest standards for dinnerware.

Microbial ContaminantsPhysical and chemical contaminants do

not change the food itself. They are potentialhazards when consumed with the food. Whenundesired changes occur in the food itself, thefood is considered to be spoiled.

Most of the time, a food is described asspoiled when its appearance, texture, flavor,or odor has changed. You would say a tomatois spoiled if it has black fuzzy patches on it.You probably would not choose to eat amushy apple over a crisp one. You would notbe likely to drink your milk at lunch if it has abad odor. You probably would not eat manypotato chips if they have a rank flavor. Each ofthese is an example of food spoilage. Foodspoilage is a change in a food that makes itunfit or undesirable for consumption. Foodspoilage occurs when a contaminant or natu-rally occurring enzymes cause the food todeteriorate or change in undesirable ways.You read about food spoilage as the result ofenzymatic changes in Chapter 12.

This chapter will look mainly at micro-organisms that cause food spoilage. You knowthat bacteria, fungi, and mold can cause desir-able changes in food. They can also causeundesirable changes. Often enzymes andmicroorganisms work together to spoil food.Softening caused by enzymes can make iteasier for molds and bacteria to enter and feedon a food product. See 18-3.

Health TipTo avoid risk of lead contamination, lookfor labels ensuring that ceramic cookwareand dishes are lead free. When serving hotbeverages, make sure you are using lead-free cups.

Tabletops Unlimited

18-2 Glazes used on commercially made ceramicdinnerware are regulated for lead safety. However,you may want to use handmade and hand-painteditems for decorative purposes only unless theyare labeled lead free.

Signs of Spoilage

� discoloration

� off odor

� fuzzy growth on the surface

� slimy feel on the surface

� foaming or gas bubbles in the product

� bulging or corroded can

� cloudy appearance

� off flavor

� mushy texture

� soft spots or breaks in the skin on fruitsand vegetables

If you suspect a food is spoiled, DO NOTTASTE IT.

18-3 This list describes noticeable changes infood or food packaging that indicate food spoilagehas occurred. However, note that some foods inearly stages of spoilage may not exhibit any ofthese signs.


Many changes in food caused by spoilagemake the food unpleasant to eat. This does notnecessarily mean the food is unsafe. However,microorganisms often bring about unpleasantchanges in food that can also cause illness. Asickness caused by eating contaminated foodis called foodborne illness.

Types of Foodborne IllnessMany people who think they have “stom-

ach flu” are really sensing the symptoms of afoodborne illness. These symptoms ofteninclude diarrhea, stomach cramps, and vomit-ing. There are approximately 76 million casesof foodborne illness each year.

An outbreak of foodborne illness is easierto detect when two or more people have thesame symptoms. However, some people aremore sensitive than others to foodbornepathogens. Therefore, two people can con-sume the same contaminated food, but theymay not both become sick.

Most cases of foodborne illness are a resultof pathogens in food. Pathogens are microor-ganisms that can cause illness in humans. Thepathogens that cause foodborne illness do notnecessarily cause undesirable changes in food.Many times, pathogens cause a food to beunsafe to eat before there are any visible signsof spoilage. Pathogens can cause illness in oneof two ways: intoxication or infection.

Food IntoxicationSome microbes can give off a by-product

that causes illness. Substances released bymicrobes that are harmful to humans are calledtoxins. In this case, it is not the microbe thatmakes people sick but the toxin it produces. Afoodborne illness caused by a toxin released bymicrobes is called a food intoxication.

It is important to remember that killing themicrobes may not be enough to prevent casesof food intoxication. If the toxin is still presentand has not been damaged or altered, the per-son will still become ill. The severity of the ill-ness will depend on the amount of toxinspresent in the food eaten. It will also dependon how susceptible the person is to illness.

A number of microbes cause food intoxica-tion. The following sections discuss those thatcause some of the most common illnesses.

Clostridium PerfringensThe bacterium Clostridium perfringens

causes one of the most frequent and, fortu-nately, mildest forms of food intoxication. Thisgram-positive microbe is anaerobic, but it sur-vives in an oxygen environment. Its spores arevery heat resistant, and small numbers oftenremain in cooked foods, 18-4. These organismscan multiply to toxic levels during cooling andstorage of prepared foods. C. perfringens iswidespread in nature. It is found in soil, water,air, sewage, and on many food products.

Foodborne illness caused by C. perfringensis often traced to eating protein-based foods.This is because of changes these foods cause inthe pH of the stomach. The low pH of stomachacid will normally kill C. perfringens. How-ever, consumption of protein foods raises thestomach pH. This rise in pH allows the moreacid-resistant spores to survive and enter theintestines, where conditions allow rapidgrowth. The toxin is a protein that is part ofthe spore coat. It causes fluids to move into theintestines. Enzymes released by C. perfringensdamage the cells of the lining of the smallintestine.

18-4 To prevent C. pefringens from multiplying, itis important to keep meats, gravies, and stuffingshot (above 60°C, 140°F) during serving.


Onset of the illness can occur anywherefrom 2 to 29 hours after eating contaminatedfood. Symptoms include diarrhea, which is aresult of the toxin pulling water into the intes-tines. The by-products of the pathogeninclude acids and large amounts of gas, whichcause bloating and cramps. The symptomslast for 12 to 24 hours. A person with this ill-ness can usually return to normal activities thenext day. Because recovery rarely requiresmedical help, many cases go unreported.Death rarely occurs unless a person is alreadyweakened by other illnesses.

Outbreaks of C. perfringens usually occurwhere large volumes of food are prepared atone time. Examples include catering services,hospitals, nursing homes, and school andworkplace cafeterias. Protein-based foodsinvolved in outbreaks have often been pre-pared a day or two in advance and thenchilled. Large amounts of food are slow to chilland allow for rapid growth of the bacteria.

Controlling C. perfringens can be accom-plished in three ways. First, food handlersmust limit contamination. Preventing contam-ination is very difficult, but following sanita-tion procedures helps limit microbe popula-tions. It takes a large number of C. perfringenscells to cause illness. The body is usually ableto handle small amounts at a time.

The second method for controlling this ill-ness is to prevent growth. Refrigeration tem-peratures slow the growth of C. perfringens,and most of the cells are killed when frozen.Maximum growth occurs at 50°C to 52°C(122°F to 125°F). Therefore, keep heated foodswell above these temperatures. Place leftoversin shallow containers. Place the containers in abath of water and ice so food will quickly dropbelow 50°C (122°F). Then place the leftovers inthe refrigerator for storage.

The third way to control C. perfringens is todestroy the organism. Cooking easily killsactive cells. Over 99% of the cells were killedin beef cubes held at 53.3°C (127.9°F).However, some spores are so heat resistantthat food would be destroyed before thespores were. Therefore, it is safest to assumethat spores have survived the cookingprocess. Gravies and sauces that may be con-taminated need to be reheated by boiling for

10 to 15 minutes. Always throw away foodthat has not been properly heated or cooled.

Staphylococcus AureusStaphylococcus aureus is a gram-positive

bacterium that occurs singly, in pairs, and inclusters. These bacteria can survive in aerobicor anaerobic conditions. They do not competewell with other bacteria. This means whenother bacteria are present, S. aureus will notgrow rapidly. Most strains of S. aureus willgrow in salt solutions that kill or stop otherbacteria. This is why S. aureus is a commoncause of foodborne illness traced to curedmeats. Pasteurization and reheating will killS. aureus. However, the toxin it produces ismore heat stable and can still cause illness afterthe microbe has been destroyed. Therefore, it isnecessary to prevent contamination with andgrowth of the microbe to avoid illness.

S. aureus is found on healthy humans andmost warm-blooded animals. It is found inpimples, boils, and open wounds. It is also onthe skin and mucous membranes, such as thelining of the nose. The bacteria are easilytransferred to the hands by touching infectedsurfaces, such as blemishes, the nose, or soiledtissue.

Growth of S. aureus occurs most rapidly attemperatures of 33°C to 38°C (91°F to 100°F).It takes about 3 hours at room temperatureafter contamination has occurred to produceenough toxin to cause illness. The illness usu-ally begins within 30 minutes to 8 hours aftereating the contaminated food. The symptomscan include nausea, diarrhea, vomiting, andabdominal cramps. The illness is rarely fataland lasts only one to two days. The severity ofthe illness will depend on the amount of foodconsumed and the individual’s resistance tothe toxin.

Foods most likely to be contaminated withS. aureus include red meats, especially ham.Poultry; potato, macaroni, and tuna salads;and custard- or cream-filled bakery productsmay also be involved in S. aureus contamina-tion. In most cases, the food is contaminatedafter it is cooked. See 18-5.

Humans are the main source of S. aureus.Therefore, monitoring the health, hygiene,and work habits of food handlers is the best


prevention method. Anyone who has exces-sive acne, infected cuts, or symptoms of thecommon cold should not handle food. Foodhandlers should frequently wash their handsand avoid touching their faces while workingwith food. Cleaning and sanitizing equipmentis also important. S. aureus can be transferredfrom humans to work surfaces and then toany food that touches those surfaces.

Controlling S. aureus means rapidly cool-ing susceptible foods or serving them quickly.Any susceptible food should be placed in con-tainers that are no more than three inchesdeep for rapid cooling. Foods should reacha temperature of 4°C (40°F) within fourhours. Foods that may be contaminated withS. aureus should not be eaten. This is because,although reheating will kill the bacteria, itdoes not destroy the toxin that causes illness.

Clostridium BotulinumUnfortunately, the third most common

source of food intoxication can be extremelydangerous. C. botulinum is a gram-positive,rod-shaped, anaerobic bacterium. It is com-monly found in all soil types and in the sedi-ments of marshes and lakes. Fish have beenfound to be carriers. The bacteria can live in fishintestines but do not multiply there. Becauseof their presence in soil, C. botulinum are com-monly found on the surface of vegetables.

C. botulinum produce a toxin called botulin,which passes through the intestinal wall and

enters the bloodstream. It then travels to nervecells. The presence of the toxin at nerve fiberjunctions will prevent nerve impulses frombeing transmitted. This results in paralysis ofthe muscles.

Foodborne illness caused by C. botulinumis called botulism. Symptoms can appear any-where from 12 to 24 hours after eating a con-taminated food. The first signs of botulism areblurred vision; progressive weakness; andred, sore mouth, tongue, and throat. Thepatient may also experience diarrhea followedby constipation and abdominal pain. Paralysisbegins in the throat and progresses to thechest, arms, and legs. The patient needsprompt medical attention to avoid death dueto suffocation. The sooner treatment begins,the better the chance of survival.

Infants up to 12 months of age are more sus-ceptible to botulism than people in other agegroups. Honey can be a source of C. botulinumspores and should never be fed to infants.Spinach, which can promote the growth ofbotulism, is another high-risk food forinfants. Some studies indicate 5% of infantswho reportedly died of sudden infantdeath syndrome (SIDS) were infected withbotulin.

Most cases of botulism are caused byhome-canned foods that were improperlyprocessed, 18-6. Other likely sources of botu-lism are improperly processed peppers,soup, asparagus, mushrooms, spinach, andripe olives.

18-5 Some cases of illness caused by S. aureushave been traced to cream-filled pastries.

USDA

18-6 Green beans canned at home need to beprocessed in a pressure canner to avoid risk ofClostridium botulinum.


C. botulinum need a pH of 4.6 or greaterand an oxygen-free environment to multiply.The bacteria grow best between the tempera-tures of 25°C and 37°C (77°F and 99°F).

Prevention of botulism begins withwashing vegetables to remove soil and asmany C. botulinum organisms as possible. Fishshould be carefully gutted and thoroughlywashed. Growth of C. botulinum can be pre-vented by freezing food.

Care needs to be taken when processingand preparing home-canned foods. This isespecially true of low-acid foods, such as cornand green beans. The spores of C. botulinumcan survive temperatures in excess of 100°C(212°F) for several hours. Therefore, low-acidfoods need to be processed at a temperatureof 121°C (250°F) to destroy the spores. (Thetoxins are destroyed at lower temperaturesthan the spores.) It is recommended that low-acid canned foods be heated to boiling (100°C,212°F) after opening. Before these foods areeaten, they should be simmered for 10 to 15minutes to guarantee the toxin has beendestroyed. Home-canned low-acid vegetablesshould never be eaten cold.

Cured and processed meats would beruined at temperatures high enough todestroy C. botulinum spores. Therefore, chem-icals must be used to destroy botulism inmeat products. Cases of botulism have beentraced to chicken liver pâté, luncheon meats,ham, sausage, lobster, and smoked and saltedfish. Sodium nitrite can be added to thesefoods to fix the color and prevent growth of C. botulinum.

Escherichia ColiEscherichia coli are gram-negative, rod-

shaped bacteria that live in the colons of mammals. They are transported to the foodsupply by sewage-contaminated water orinfected food handlers.

There are four strains of E. coli that areknown to cause foodborne illness. One straincauses illness when present in large numbersin the small intestine. A second strain seems toproduce a toxin while in the small intestine. Athird strain invades the mucous lining of theintestines. A fourth strain causes bleeding inthe colon and kidney failure. This last strain is

the deadliest, especially among small childrenand older adults. It can cause illness with asfew as 10 cells in the food supply.

The time from exposure to onset variesfrom less than 1 day to 13 days. Most patientsbegin to exhibit symptoms between 18 and 44hours after eating the contaminated food. Theillness usually lasts from 3 to 4 days. The mainsymptom is diarrhea, but nausea, fever,cramps, weakness, aches, and vomiting mayalso occur. Treatment centers on replacing flu-ids and electrolytes.

Outbreaks of E. coli have occurred as aresult of consuming soft cheeses, hamburgers,salads, and apple juice. Any food exposed toraw fecal matter is at risk of being contami-nated. Ground meats are at risk because thegrinding process can mix any E. coli presentthroughout the meat. Any patty not cookeduntil done would then have E. coli present inthe center of the meat. See 18-7.

Steps for preventing contamination can betaken by communities as well as by indivi-duals. Communities chlorinate water suppliesto eliminate harmful bacteria. Anyone han-dling food must thoroughly wash his or herhands after using the bathroom. People who

18-7 Hamburgers and other ground meat productsneed to be cooked to an internal temperature of71°C (160°F). This will kill any E. coli that may bepresent.


cook ground meat must be sure to cook itthoroughly. These efforts will help reduce therisks of an E. coli outbreak.

Food InfectionThe second major cause of foodborne ill-

ness is the microbes themselves. Microbesrelease digestive enzymes that begin to dam-age body tissue and cause illness. This type offoodborne illness is called food infection. Afood infection cannot occur if the microbes arekilled.

Food infections may be caused by bacteria,parasites, and viruses. A large number of liv-ing organisms is usually required to cause ill-ness. Symptoms are related to damage causedby the organisms feeding on their hosts.

Listeria MonocytogenesListeriosis is a foodborne infection caused

by Listeria monocytogenes. This is a rod-shaped, gram-positive bacterium. It is foundin soil, water, and many species of animals.Food sources include soft cheeses, uncookedmeats, unwashed vegetables, and unpasteur-ized milk.

L. monocytogenes is harder to kill thanmany other foodborne pathogens. It can grow

and multiply at refrigerator temperatures. It isaerobic, but it grows best at reduced oxygenlevels combined with increased carbon diox-ide. It can grow in 10% salt solutions and at apH of 9.

Symptoms of listeriosis include fever,headache, nausea, diarrhea, and vomiting.Listeriosis can also cause infections in preg-nant women, which can result in miscarriageor stillbirth. Nearly 25% of serious cases resultin death.

Those at greatest risk are pregnantwomen, newborns, and people with weak-ened immune systems, including many olderadults. General guidelines for reducing therisk of listeriosis include thoroughly cookingraw meat and poultry and carefully washingraw vegetables. In addition, people in high-risk groups should avoid eating soft cheeses,such as feta, Brie, and blue-veined cheeses.Those at risk should also heat all precookedfoods and processed meats, such as deli meatsand hot dogs, until they steam. See 18-8.

SalmonellaeSalmonella is a genus of rod-shaped, gram-

negative, anaerobic bacteria. These microbescause an illness called salmonellosis. The bac-teria attach to the lining of the intestines and

In October 1996, an outbreakof E. coli infection occurred in thewestern United States. Thirteencases of E. coli infection weretraced to unpasteurized applejuice packaged by Odwalla AppleJuice. The company recalled alldrinks that contained apple juice.

In July 1997, an outbreak ofE. coli infection occurred inColorado. The ColoradoDepartment of Health andEnvironment traced this outbreakto frozen hamburger patties fromHudson Foods Company. Thesource was believed to be meat

grindings. Apparently leftovermeat grindings from one day’sprocessing had been saved andused the next day. The FDA con-ducted further investigation. Thisled the FDA to order a recall of 25million pounds of hamburger pro-duced by a Hudson Foods plant.

Item of InterestOutbreaks of E. coli


release digestive enzymes. These enzymesdamage the tissue of the intestinal lining. Ittakes a large number of salmonellae to causesymptoms. However, a small number of bac-teria can attach to the intestines and reproduceuntil illness results. Body fluids are pulledinto the intestines, which causes diarrhea.Other symptoms include cramps, fever, nau-sea, vomiting, chills, and headache. Treatmentincludes giving fluids to prevent dehydration.Use of antibiotics has no noticeable benefitand leads to strains of salmonella that areresistant to antibiotics.

Less than 1% of all reported cases of sal-monellosis end in death. This makes salmo-nellosis far less dangerous than botulism.However, there are so many cases of salmo-nellosis that far more people die from it thanfrom botulism. Young children, older adults,and people with other illnesses are at thegreatest risk.

The time between eating a contaminatedfood and the onset of salmonellosis is generally

6 to 48 hours. Symptoms in adults usually lastonly 2 to 3 days. However, symptoms may lastlonger in children.

The Centers for Disease Control estimatethat eggs are involved in about 75% of allsalmonellosis outbreaks. Other foods mostlikely to be contaminated with salmonellae arepoultry, beef, dairy products, and pork.Poultry and livestock producers are workingto reduce the number of salmonellae thatoccur in animals before and during slaughter.

Poultry and poultry products are majorsources of salmonellae for two main reasons.The first is that salmonellae live in poultrywithout causing the birds to become sick. Thesecond is the broad use of antibiotics in poul-try feed to increase poultry production. Manyof the strains of salmonellae that commonlycause illness are resistant to antibiotics.Salmonellae also multiply quickly when othermicrobes have been killed or reduced in num-ber by antibiotics.

Care needs to be taken to prevent salmo-nellae contamination during food preparation.Salmonellae are often spread from one foodto another by food handlers. These bacteriacan survive on people’s hands for hoursbefore being transmitted to foods where theywill thrive and multiply. Therefore, foodhandlers should keep work surfaces andhands clean.

To prevent salmonellae growth, cold foodsneed to be kept cold, and hot foods need to bekept hot. Salmonellae grow very quicklybetween 10°C and 50°C (50°F and 122°F). Whenheating and chilling, foods need to be movedthrough this temperature range as quickly aspossible. Foods that are cooked just beforeeating will usually be free of salmonellae.

Care must be taken to cook ground meatand poultry until they are thoroughly done.When meat is ground, the salmonellae can bemixed all through the meat. If hamburgers arestill pink in the middle, salmonellae could stillbe alive in the center of the patty. Poultryshould always be cooked until the juices runclear. See 18-9.

Raw or improperly cooked eggs are apotential hazard. Many uncooked recipes forhomemade ice cream, Caesar salad, hollan-daise sauce, and mayonnaise call for raw eggs.

18-8 People in high-risk groups for foodborne illness should heat cold cuts until they are steaming hot to reduce possible exposure to L. monocytogenes.


Pasteurized eggs should be used in place ofraw eggs in these dishes. Pasteurized eggshave been heated to kill bacteria such as sal-monellae. Shell eggs should be cooked untilthe yolk is thickened and the white is firm.Scrambled eggs should be cooked until theyare no longer runny. See 18-10.

Parasitic InfectionsMost of the pathogens that cause food-

borne illness are bacteria. However, some ill-nesses are caused by parasites. Parasites areorganisms that live in and feed on a host. Ahost is an animal or plant from which a para-site receives nutrients. Some parasites thatcause foodborne illness are commonly foundin contaminated water supplies. Raw fish canbe sources of these parasites. Fresh fruits andvegetables cleaned with contaminated watercan be sources, too. Hogs, cattle, and wildanimals are common hosts of other illness-causing parasites.

Trichinella SpiralisTrichinella spiralis is probably the best-

known parasite that causes foodborne illness.This parasite is a microscopic roundworm. Itoccurs in hogs and wild animals, such asbears, boars, and rabbits. Humans can alsoserve as hosts of T. spiralis. This parasite canenter a host as adult worms or larvae throughinfected food. Larvae are immature parasitesthat are often surrounded and protected by acyst, or pocket. Within the host, digestionbreaks down the cysts, releasing the larvaeinto the host’s small intestines. The larvae feedand grow into adult roundworms. The adultworms attach themselves to the intestinalwalls, where they produce new larvae. Thenew larvae penetrate the intestinal walls andtravel in the bloodstream to muscle tissue.Once imbedded in the muscle, the larvae formprotective cysts. T. spiralis can survive foryears in the muscle tissue of the host.

An infection caused by T. spiralis is knownas trichinosis. During the first phase of the illness, the symptoms include nausea, abdom-inal pain, and diarrhea. Once the larvae enterthe muscle tissue, symptoms will includemuscle pain and fever.

Prevention is the best protection againsttrichinosis. T. spiralis larvae are destroyedwhen meats are adequately cooked. Curing,smoking, and fermenting processes will alsodestroy the larvae. Pork used to be the mostwidely eaten source of this parasite.Inspection and production procedures haveeffectively eliminated T. spiralis from commer-cial pork, 18-11. The USDA has recommendedprocessing procedures that should destroyany T. spiralis in cured pork products. Themain source of T. spiralis in the United Statestoday is game meats. Like pork, fresh game,such as bear, boar, and rabbit, should always

Recommended Cooking Times for Eggs

Sunny side up

Over easy

Poached

7 minutes, uncovered4 minutes, covered

3 minutes on one side then 2 minutes on the other side

5 minutes in boiling water

18-10 Salmonellae are destroyed when egg dishes reach an internal temperature of 71°C (160°F).

USDA

18-9 Checking poultry with a food thermometerensures the internal temperature is high enoughto kill any salmonellae that may be present.


be cooked to an internal temperature of 71°C(160°F). Freezing will kill the larvae if the meatis held at -15°C (5°F) for at least 30 days.

Viral InfectionsViruses are a third type of pathogen that

can cause foodborne illnesses. A virus is amicroscopic disease-causing agent made up ofgenetic material surrounded by a protein coat-ing. The protein coating is called a capsid.Viruses do not multiply in food, but someviruses can be transmitted in food.

A virus must attach to a host cell. Geneticmaterial from the virus is injected into the hostcell. The genetic material can attach to the hostcell’s genes. This causes the host cell to makemore virus particles. Eventually the large num-ber of virus particles causes the host cell to rup-ture and die. The virus particles are then freedto find new host cells and repeat the process.The nature of viral infections is related to whichcells the virus can attach to and destroy.

Health experts do not know how manyvirus particles a person must ingest for illnessto occur. This is because viruses are difficult todetect in food. Experts do know that virusesmust survive stomach acids and digestiveenzymes for any illness to develop. Studieshave found that viruses remain stable and

able to contaminate food in a wide range ofsituations. For instance, poliovirus was foundon fruit and vegetable crops fertilized withcontaminated sewage sludge. This virus wasable to survive on the fruits and vegetables upto 36 days. Viruses can also survive� on glass, stainless steel, and tile for up to

eight weeks at room temperature� on low-moisture foods for over two

weeks at room temperature and morethan two months when refrigerated

� in ground meat for 8 to 14 days at 4°C(39°F)

Poultry and poultry productshave been identified as majorsources of salmonellae contami-nation. Statistics from theCenters for Disease Control alsoshow outbreaks in which beefand veal are the sources. (Anoutbreak is when two or more

people are known to become illfrom eating the same food.) Thereason for this is that chicken isusually eaten well done.However, many people eat beefand veal rare.

In outbreaks in which the foodsource was identified, 80% were

caused by undercooked or raweggs. In August 1990, the FDAreleased recommendations forthe use of eggs in all commercialfood settings. These recommen-dations include using pasteurizedeggs in place of shell eggswhenever possible.

Item of InterestSalmonellae—Who’s theCulprit?

USDA

18-11 Hogs are inspected to ensure they are freeof Trichinella spiralis.


Viruses are usually transmitted throughthe fecal-oral route. This refers to the con-sumption of any food or beverage that hascome in contact with feces. A viral infectioncan be transmitted from contaminated fecesto food in two main ways. The first is failingto wash hands after going to the bathroomand then handling food. The second is usingsewage-contaminated water or fertilizer onfood crops.

Four main types of viruses have beenfound to cause foodborne illness. Theseinclude Rotavirus, Norwalk virus, and hepati-tis. Threat of the fourth type, poliovirus, haslargely been eliminated in the United Statesby vaccinations.

RotavirusRotavirus occurs most often in young chil-

dren. By age five, most children have beeninfected with this virus and developed immu-nity. Flulike symptoms, including vomiting,diarrhea, and low-grade fever, will last for 2 to10 days. This viral infection is most commonduring winter months. Good hygiene prac-tices are the best prevention. Any food han-dled by an infected person and then eatenwithout further cooking is a potential risk.

Norwalk VirusNorwalk virus is named for the first docu-

mented outbreak, which occurred in 1968among school children in Norwalk, Ohio. Thisvirus causes a mild flulike illness that lasts oneto two days. It occurs among all age groupsand during any time of the year. Outbreakshave been traced to green salads, raw oysters,cake frosting, and chicken sandwiches.Humans are the only carriers. Preventioninvolves good personal hygiene. It is alsoimportant that people with any flu or coldsymptoms avoid handling or preparing food.

HepatitisHepatitis is a viral infection that attacks

the liver cells. Hepatitis A, or infectious hepatitis,is the strain of hepatitis that can be trans-mitted through contaminated food. Flulikesymptoms will last for one to three days.Three to four weeks later, symptoms of liverinfection develop. Cases are usually mild.

More severe infections can lead to liver failureand death.

Hepatitis A is destroyed when food iscooked. Foods at risk are uncooked saladingredients, raw shellfish, and any foodrequiring handling after cooking. People whobuy shellfish should make sure the seafoodhas come from clean waters that are free fromraw sewage. Shellfish should not be eatenraw. Clams dropped in boiling water untilthey opened seemed to be the cause of onehepatitis outbreak. This indicates that limitedheating is not sufficient to destroy the virus.See 18-12.

Most outbreaks of hepatitis have beentraced to infected food handlers. Infected foodhandlers can transmit hepatitis for 7 to 10 daysbefore they develop any symptoms. Therefore,food handlers need to monitor their health andwash their hands frequently to help preventthe spread of hepatitis. They should also weardisposable gloves when handling foods justprior to serving. Anyone who has beenexposed or is at risk of exposure can be given avaccine called immune serum globulin.

USDA

18-12 Commercially raised clams are tested formicrobial contamination as an important part ofthe inspection process.


How Pathogens Enter the FoodSupply

Why is there a problem with pathogens inthe food chain? One reason is the developmentof new, hardier strains of microbes. The speedwith which bacteria reproduce enables newstrains to develop quickly. A genetic change ina bacterium takes less than 24 hours to appearin thousands of new bacteria. By contrast, agenetic change in a human takes aroundtwenty years to appear in a few children.

New strains of microbes develop due tominor genetic differences in a small percent-age of microbes. For instance, when antibioticsare given to chicken, most of the bacteria pres-ent are killed. However, a small percentage ofthe bacteria has some minor difference. Thismakes them harder to kill and allows them tosurvive. These bacteria will reproduce. Theresult will be a new strain of bacteria that isresistant to the antibiotic. New strains ofmicrobes that withstand higher temperatures,lower pH ranges, or different air mixes devel-op in the same way.

It is important to understand howmicrobes can get into the food supply. Thereare two main ways food can become con-taminated with pathogens. Pathogens canbe transmitted by animals and throughimproper handling procedures.

Transmission by AnimalsYou may have noticed that many of the

foods linked to food infections and food intox-ications are from animal sources. Animals arehosts or carriers for many microbes. Protein-based foods from animal sources also providean environment in which microbes can growand multiply.

Warm-Blooded Animal CarriersAll warm-blooded animals have microbes

living in and on them. Animals can transferthese microbes to food products. One way thiscan happen is by allowing food products tocome in contact with animal feces.

An example of this is found in apple juicecontaminated with E. coli bacteria. One waythis juice might have been contaminated is bydeer. E. coli live in the colons of humans and

other mammals, including deer. If E. coli enterthe stomach and small intestines, they cancause illness. In the colon, however, these bac-teria help break down waste products. E. colican be passed out of the body in feces.

Deer will feed on apples that grow on thelower branches of apple trees. Deer alsoexcrete in apple orchards while eating. Applesthat fall from the trees may come in contactwith deer feces. These fallen apples are likelyto be bruised and will quickly spoil. They can,however, be pressed to make apple juice. Theapples need to be thoroughly washed or thejuice needs to be pasteurized. Otherwise,the apple juice can become contaminatedwith E. coli from the deer feces.

Another way microbes from animals canend up in foods happens when the animals areused as meat sources. During slaughter andpackaging, microbes on the surfaces of an ani-mal are often transferred to the cuts of meat. Ifthe meat is not properly handled and pre-pared, it can become a source of foodborne ill-ness. See 18-13.

Raw FishVarious parasites live in fish and shellfish.

If the fish is eaten raw, these parasites can enterthe digestive tract, causing illness and death.Popular raw fish dishes that are at risk of caus-ing illness include sushi, oysters, clams, andmussels. The FDA has recommended a proce-dure for fish that will be consumed raw. The

USDA

18-13 Store raw meats and poultry on trays in therefrigerator to avoid contaminating other foodswith dripping juices.


fish should be quick-frozen to -35°C (-31°F) for15 hours. The fish can also be held in a com-mercial freezer at -20°C (-4°F) for 24 hours.The fish may then be thawed and eaten.

Meat and Dairy ProductsMeats, milk, and eggs are often associated

with foodborne illness. There are three keyreasons for this. First, these foods all provide amedium in which microbes can thrive.Second, these are popular foods that arewidely consumed in the U.S. diet. Third,many people are uninformed about how tohandle these foods to prevent illness. Forexample, some people believe raw eggs are ahealthful ingredient in a protein shake. Thesepeople are unaware that salmonellae can getinto an egg before the shell is formed. They donot realize that drinking a shake containingraw egg puts them at risk for salmonellosis.

Avoiding food from animal sources is nota wise way to prevent foodborne illness.These foods are important sources of nutrientsin the diet. Learning how to properly handlethese foods is a more appropriate preventionstrategy.

Improper Handling ProceduresOnce food is contaminated, improper han-

dling can allow the microbes to multiply andcause illness when eaten. Improper handlingprocedures can be divided into three groups.� time and temperature abuse� poor personal hygiene� cross-contamination

Time and Temperature AbuseThe number one cause of foodborne ill-

ness is the failure to properly cool food. Mostpathogens multiply rapidly between 4°C and60°C (40°F and 140°F). This temperaturerange is referred to as the temperature dangerzone. Foods at risk for pathogens should bekept cold or hot during storage, transporta-tion, preparation, holding, and service. Allrefrigeration units must be below 4°C (40°F)and heating units must be at or above 60°C(140°F). As a rule, the total time a perishablefood is in the danger zone should not exceedtwo hours. This time includes mixing time at room temperature, standing time before

or after cooking, and holding time duringmeal service.

Poor Personal HygieneThe food industry works hard to provide a

safe food supply that is as free from contami-nants as possible. The FDA, EPA, and USDAinspect and monitor the food supply. Theystrive to protect consumers from contaminantsduring the growth, production, and processingof food. However, food handlers and cus-tomers are one of the major causes of unsafefood. Sources of human contamination includehands, breath, hair, wounds, unshieldedcoughs and sneezes, and perspiration.

Cross-ContaminationCross-contamination occurs in food

when a contaminated substance comes incontact with another food. Any surface thatcomes in contact with food will cause cross-contamination if microbes are present. Forexample, suppose you use a cutting board fordeboning and slicing a raw chicken breast fora stir-fry. Salmonellae are on the surface of thechicken. The salmonellae get on the cuttingboard. You give the board a quick rinse withwarm water. You then use the board to sliceraw vegetables for a salad. The salmonellaewill be transferred from the cutting board tothe salad ingredients. Although salmonellaeon the chicken will be killed during cooking,the salad is not cooked prior to eating. See 18-14. Cross-contamination can also occurwhen plant foods are harvested and come incontact with the soil around them.

Uninformed or Careless ConsumersAll three major causes of foodborne illness

are related to uninformed and careless con-sumers and food handlers. It does not matterwhether food is contaminated by improperheating, poor personal hygiene, or cross-contamination. The result is illness for anyonewho eats the contaminated food. It is impor-tant to remember that pathogens can makepeople ill long before the food will show signsof spoilage.

Any food, if improperly handled, cancause foodborne illness. The leading cause of food-related illnesses is consumers andfood handlers who are ignorant or careless. A


certain hunter is an example of a consumerwho was ignorant of the dangers associatedwith eating some foods. This hunter decidedto feed bear meat to friends at a cookout. Thehunter mixed the bear meat with ground beefto conceal the taste. He did not tell anyonethat part of the meat came from bear. Thosewho chose to have their burgers cooked to thewell-done stage were fine. Those who chose tohave their burgers cooked to the rare or medi-um stage became ill. In this case, the hunterdid not know that bear meat is often contami-nated with parasites. The guests were unin-formed as to what they were eating.

The school cafeteria workers mentioned atthe beginning of the chapter are an example ofcareless food handlers. The health departmenttraced the illness to a potato salad made by acafeteria worker trained in food safety. Theworker had made the potato salad for apotluck luncheon held to honor retiring cafe-teria workers. The worker left the potato saladon her kitchen table while she dressed for thepotluck. Then she left the salad in her hot carwhen she made some stops on the way to theluncheon. (The temperature in a closed car ona hot, sunny day can quickly exceed 38°C,100°F.) At the potluck, the potato salad wasplaced on the serving table almost an hourbefore everyone was served. By the time thesalad was eaten, it had been at or above roomtemperature for over two hours. Half of thecounty cafeteria workers ate some of the

salad. Those who ate the salad were too sick toreport to work the next day. This type of prob-lem can easily occur at picnics, communitydinners, church potlucks, restaurants, andfamily gatherings.

Food Industry SanitationProcedures

Monitoring the safety of the food supplyinvolves two key aspects. The first is a volun-tary effort by the food industry to set and follow standards that will help prevent con-tamination. The second part of the monitoringprocess is government regulation.

Developing a HACCP SystemThe food industry works with govern-

ment agencies to set up guidelines that willprevent contamination or growth of microbesin foods. The food safety system used mostoften by U.S. food producers is called HACCP(Hazard Analysis and Critical Control Point).A HACCP system looks at every point in thefood production process where contaminationcan occur. This system views a hazard as any-thing that could cause harm. Hazards includemicrobes, toxins, chemicals, and foreignobjects in food. A critical control point is anypoint in a food operation where hazards canbe removed, prevented, or minimized.

Meat and fish producers became requiredto phase in HACCP systems between 1998and 2000, 18-15. The FDA published rulesmandating HACCP for fruit juice producers inJanuary 2001. For producers of other foodproducts, HACCP is voluntary. However,

Storage TipsObserve the following precautions toreduce the risk of foodborne illness:

� When in doubt, throw it out!

� Use older foods first. (Remember thistip by the acronym FIFO, which standsfor first in, first out.)

� Reheat leftovers only once. Discardany uneaten reheated food.

� Use refrigerated leftovers within threeto four days.

USDA

18-14 To prevent cross-contamination, be sure tothoroughly wash cutting boards, knives, andhands after preparing poultry before handlingfresh vegetables.


many food producers choose to use a HACCPsystem because it reduces the producer’s riskof liability. HACCP also increases profits byworking to prevent outbreaks of foodborneillness.

The HACCP concept was originated byNASA and Natick Laboratories in the 1960s.Pillsbury worked with NASA and NatickLaboratories to develop the HACCP systemin 1971. The system was designed to be flexi-ble enough to adapt to any aspect of the foodindustry. It can help prevent contaminationat any stage from growing crops to servingthe food.

Developing a HACCP system involvesseven main steps. The first step is to deter-mine potential hazards. Is the company work-ing with high-risk foods, such as meat, poul-try, seafood, or egg and dairy dishes? Howdoes food move through the system? Whereand how is it stored or packaged? When doesit come in contact with humans, chemicals,and machinery?

The second step is to develop a flowchartfor each procedure in the company, plant, orrestaurant. Each point in the process wherehazards can occur is identified.

The third step is to set standards that areneeded at each control point. Standards mustbe specific and measurable. This step alsoinvolves determining procedures for main-taining the standards. Examples include mon-itoring temperatures of heating and coolingunits, identifying cooking times, and definingcleaning procedures. Employees must betrained to follow procedure directions exactly.

Step four is to monitor the critical controlpoints. Regularly checking equipment foraccuracy and keeping thorough records ofprocedures are part of this process.

The fifth step is to correct any problems assoon as they are discovered. For example, chiliis to be held at 60°C (140°F) until it is served.A supervisor performs a temperature checkand discovers the chili is at 57°C (135°F). Thesupervisor then checks the records to see howlong the chili has been on the holding unit. Ifthe chili has been held for longer than twohours, it is discarded. If the holding time isless than two hours, the chili is immediatelyreheated to 74°C (165°F) for 15 seconds.

Step six is keeping records. Procedures areto be clearly written and posted. Time andtemperature logs are dated and kept for eachbatch of food prepared or processed. Theserecords provide legal verification of proce-dures used.

The last step is to have the HACCP systemverified once it is in place. This is usually doneby an official inspector from the FDA, USDA,or local health department.

HACCP in the Meat IndustryBeef Products, Inc. is one of the world's

leading producers of boneless lean beef. TheirHACCP system is a 24-hour process. A sampleof finished product is pulled from the lineevery 10 seconds. A sample is pulled fromeach box on every pallet. Samples are com-bined from enough beef packages to fill a pal-let. This composite sample is analyzed for fat,water activity, and protein levels. Each box oneach pallet is bar coded with the date and pal-let information. Every two hours, a portion ofall samples drawn are sent to an independent

USDA

18-15 Meat producers are required to use aHACCP system to help ensure the safety of meatproducts.


lab for microbial testing. Each 2-hour sampleis tested for total plate count, E coli, coliform,Salmonella, Listeria, Staphylococcus, and E coli0157:H7. In addition, a daily composite sam-ple is sent to an independent outside lab forcentral nervous tissue testing. All packagedproducts are moved immediately after pack-aging to a 15-level cold storage unit that holdsup to 28 million pounds of meat.

Once the meat is packaged, a fully auto-mated system moves the packages throughtemperature-controlled areas. The pallet pack-ing area is held at 27°F, the holding freezer is0°F to -5°F, and the loading dock is kept at40°F. In addition, none of the meat is releasedfor shipping until all the microbial profileshave been completed and the meat is found tobe safe. No matter how thorough such aHACCP system is, the final safety of any foodproduct depends on the retailer and the con-sumer continuing to handle, store, and pre-pare all foods appropriately.

Government Regulation of the FoodIndustry

The FDA and USDA are two of the federalagencies that monitor the safety of the foodsupply. They are mainly responsible for foodproduced and shipped across state lines.These agencies set standards that often repre-sent the minimum needed for safety. Forexample, the standard for chilling a food aftercooking may be to reach 0°C (32° F) withinone hour. It is fine if the chilling time is lessthan one hour. However, it cannot exceedone hour.

Local and state health departments moni-tor foods produced and sold within states.Local health departments also regulate food-service operations. Local regulation agenciesuse guidelines established by federal and stateagencies.

Before any food business can open, itmust get a permit and be inspected. This is tomake sure safety and sanitation regulationsare being followed. Once a business is operat-ing, the FDA recommends that inspections becarried out at least twice a year. Fewer inspec-tions are needed when efficient HACCP sys-tems are in place. Violations of regulationscan result in warnings, fines, and/or closureof the business. See 18-16.

18-16 Businesses that make and sell food productsmust undergo periodic health inspections.

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Chapter 18ReviewChapter 18Review

Summary

Food becomes spoiled when contamina-tion causes undesirable changes. Spoiled foodis unpleasant but not necessarily harmful toyour health. Spoiled food has an unpleasanttaste, texture, odor, and/or appearance.Spoilage is usually a result of enzymes andmicrobes naturally found in the food.

Illness can result when foods become con-taminated with harmful substances. Somefood illness is caused by the toxins released bymicrobial action as a by-product. Both the bac-teria and the toxins produced must bedestroyed to prevent illness. Other cases offood illness are caused by the microbes them-selves. To protect your family and yourselffrom food contamination, it is helpful tounderstand the pathogens that cause illness.You need to know what they require to sur-vive, grow, and multiply. Each microbe has apreferred food source, temperature, and pHrange. This information is your best weaponfor fighting food contamination.

Pathogens have been found to enter thefood supply in several ways. The first sourceis through animal carriers. The second sourceis improper handling procedures. Unin-formed and careless consumers are a majorsource of pathogens in food.

Government agencies and the food indus-try work together to monitor and maintain asafe food supply. HACCP is an efficient foodsafety system that reduces the risk of food-borne illness and the need for frequent inspec-tions. A safe food supply requires the cooper-ation and education of everyone involved inthe handling of food.

Check Your Understanding

1. List the primary sources of contaminationand give two examples of each.

2. Describe two ways that insects androdents can damage or contaminate food.

3. Explain the difference between contami-nation, spoilage, and foodborne illness.

4. Compare and contrast the two ways thatpathogens can cause illness.

5. List four common microbes that causefood intoxication and a common foodsource for each.

6. Why are poultry and eggs the mainsources of salmonellosis?

7. Name a parasite that can cause foodborneillness and its most common food source.

8. List three viral infections that can con-taminate food

9. What are the three reasons that meat anddairy products are often sources of food-borne illness.

10. Name three basic ways that food is han-dled improperly. For each, name a safetyguideline to follow to reduce risk of food-borne illness.

11. List the seven steps of the HACCP process.12. Who is responsible for monitoring the

safety of the food supply?

Critical Thinking

1. After enjoying a buffet at a familyreunion, many guests report having diarrhea, stomach cramps, and bleedingin the colon 24 hours later. Whichmicrobe is the likely cause?

2. Why are county fair entries of low-acidcanned goods simmered for 15 minutesbefore judges sample them to select thewinners?

3. After eating Brie that has been kept wellchilled, an older adult experiences diar-rhea, vomiting, and fever. What microbeis the likely cause?

4. Why is it best to sweeten an infant’s hotbreakfast cereal with sugar rather thanhoney?

425

Explore Further

1. Math. Research the number of cases offoodborne illness last year reported bythe Center for Disease Control. Calculatethe percentage of foodborne illnesscaused by intoxication versus infection.

2. Technology. Use the computer to createan attractive, attention-getting poster orhandout on food safety procedures forthe school’s Family and ConsumerSciences food labs.

3. Writing. Write an article for the schoolnewspaper on how to safely handle andstore foods to prevent foodborne illness.

4. Application. Use the HACCP process todevelop a procedure for monitoring thesafety of the laboratory during and afterconducting this chapter’s experiments.How will you ensure that bacteria sam-ples do not contaminate surfaces that willbe used for food production by otherclasses.

5. Analytical Skills. Read a recent article onthe use of antibiotics in our society.Report how antibiotics are made, whythey become ineffective, and what yourecommend regarding the food industry’suse of antibiotics in the future.

426

PurposeMolds are found nearly everywhere. Moldsare hardier than bacteria and yeast. Theygrow over a wider range of pH and tempera-ture and at higher salt concentrations.Although molds spoil food, most are not ahealth hazard. In 1961, a mycotoxin (a toxingenerated by some molds) named aflatoxinwas discovered. Aflatoxin damages the liverand is a known liver carcinogen. These toxinsare extremely lethal and frequently heat sta-ble. Cooking mold-contaminated food willnot destroy the toxins. In this experiment, youwill examine how molds grow on foods. Thiswill help you determine the safety hazards ofunidentified molds.

Equipmentparing knifemicroscope slidesmicroscope

Supplies1 slice apple1/2 slice preservative-free bread1 slice cheese3 closed containers or resealable plastic bags

Procedure1. Cut a piece as thin as possible off slices of

apple, bread, and cheese.2. Place each sample on a microscope slide.3. Observe each sample under a microscope.

Record your observations and draw asketch of what you see in a data table.

4. Place the rest of the half slice of bread ina container or resealable plastic bag sothere are 3 to 5 cm of airspace above thebread. Seal the container and label it withyour lab group name or number.

5. Place the apple slice in a second containerand the cheese slice in a third container,just like the bread. Label both containerswith your lab group name or number.

6. Place all three containers on a table orwindow sill as directed by your teacher.

7. Each day, examine the food samples forvisible mold growth.

8. When mold is visible, use a knife to removea small piece of the aerial (above the food)mold from the bread. Place it on a slide.

9. Observe the mold under a microscope.Record your observations and draw asketch in the data table.

10. Repeat steps 8 and 9 for the apple andcheese.

11. Scrape the visible mold from the surfaceof each food.

12. Cut a thin, cross-sectional sample of eachfood.

13. Place each sample on a slide and observeit under a microscope. Look for signs ofsubmerged (under the surface) mold growthin the food. Record your observations anddraw a sketch in the data table.

14. Discard all food samples and clean allsurfaces with a sanitizing solution.

Experiment 18AMold Growth in FoodsExperiment 18AMold Growth in Foods

Safety� Do not taste any of the samples.

� Clean all surfaces with a sanitizingsolution at the end of the experiment.

427

Questions1. What texture changes occurred on moldy

samples?2. What, if any, differences were there in the

appearance of the molds on each of thethree samples?

3. How deeply does mold appear to growinto each of the three foods?

4. How can mold growth be prevented ordelayed?

428

PurposeBacteria is present everywhere. It is not visibleunless it has grown into a large colony knownas a culture. Cultures can be isolated and stud-ied by microbiologists. Bacteria is placed inpetri dishes on a substance called agar. Agarcools into a gel and contains nutrients that aidthe growth of bacteria. In this experiment, youwill collect bacteria samples and incubatethem to grow cultures.

Equipmentwax pencilincubator

Supplies1 disposable petri dish with agar per studentclear cellophane tape

ProcedureDay 1

1. Use a wax pencil to write your name onthe outside of the lid of your petri dish.Draw two intersecting lines on the bot-tom of the dish to divide the dish intofour quarters.

2. Tear off a short piece of cellophane tape.It should be long enough to fold in halfwith the sticky side out.

3. Gently press the sticky side of the foldedtape against the surface to be tested.Immediately lift the lid of the petri dish

and gently press the folded tape againstthe agar in one section of the petri dish.Quickly re-cover the petri dish and labelthe quarter on the bottom of the dish toindicate the surface tested.

4. Repeat steps 2 and 3 to test one other sur-face, as assigned by your teacher.

5. Lift the lid of the petri dish and gentlyplace your thumb on a third quarter ofthe agar. Light pressure will reveal athumbprint. Too much pressure will crackthe agar. Label this quarter unwashed.

6. Wash your hands and then place athumbprint in the last quarter of the petridish. Label this quarter washed.

7. Tape the lid onto the petri dish. Turn thedish upside down and place it in an incu-bator as instructed by your teacher.

8. Your teacher will incubate the petri dishes at 37°C for 24 to 48 hours.

Day 21. Record descriptions of the bacteria

colonies on your petri dish.2. Examine the samples prepared by your

teacher and record descriptions. One is thecontrol that did not have the lid removed.The second was left open to the air for 15minutes while samples were collected.

3. Examine the samples prepared by yourclassmates.

Questions1. What procedure did you use to wash

your hands?2. How did the culture from your

thumbprint compare to the cultures ofyour classmates’ thumbprints?

3. What, if any, difference did the hand-washing procedure used make in bacterial growth?

Experiment 18BGrowing Bacterial CulturesExperiment 18BGrowing Bacterial Cultures



429

4. Did you find any sterile surfaces (surfacesthat were free of bacteria)?

5. How easy is it to transfer bacteria fromone place to another?

6. What differences did you observebetween the control and the petri dishthat was left open for 15 minutes? Howcould a culture start to grow on the dishthat was left open?

430

PurposeBacteria are small and hard to see, even ifmagnified 1,000 times. To examine bacteria,scientists spread a mixture of bacteria and dis-tilled water on a slide to prepare a smear. Theslide is air dried before being passed over anopen flame several times to heat fix the bacte-ria to the slide. Failing to dry the slide beforeheating will cause the heated water to distortthe shape of the cells. Heating the slide alsodenatures enzymes in the cells, which pre-vents deterioration of the cells. Once bacteriaare heat fixed to a slide, they can be stained sothey are easier to see. Stains also help identifythe types of bacteria. Gram’s staining is usual-ly the first step in identifying bacteria. In thisexperiment, you will prepare slide samplesfrom the bacteria you collected in Experiment18B. After staining, you will determinewhether the bacteria is gram-positive or gram-negative. You will also identify the shape ofthe bacteria cells.

Equipmentwax pencilinoculating loopgas flame source (Bunsen burner, gas stove)1 clothespin per studentbeaker or bowleyedropper2 wash bottlesoil immersion microscope

Supplies1 new microscope slide per studentdistilled waterpetri dish with bacteria cultures from

Experiment 18B1 to 2 drops crystal violetGram’s iodineethyl alcoholsafraninmicroscope tissue paper2 drops immersion oil

ProcedurePreparing a Smear

1. Handle a new microscope slide by theedges. With a wax pencil, make a dime-sized circle in the center of the slide.

2. Sterilize your inoculating loop by holdingit over a gas flame source until the loop isred hot.

3. Using the inoculating loop, place 1 or 2loopfuls of distilled water in the center ofthe circle.

4. Sterilize your loop again. Allow the loopto cool so any bacteria you pick up with itwill not be destroyed. Cooling takesabout 30 seconds.

5. Use the sterilized loop to scrape a smallamount of one of the bacteria culturesgrown in Experiment 18B from the petridish. Mix the culture with the water onthe slide.

6. Spread the bacteria evenly within the ring.7. Allow the smear to air dry. This will take

about 2 to 4 minutes. Do not blow on theslide, as this will cause cell positions toshift.

8. After the slide is completely dry, use aclothespin to hold the slide as you pass itover the gas flame two or three times.

Experiment 18CThe Gram’s Stain Test for BacteriaExperiment 18CThe Gram’s Stain Test for Bacteria



� Dispose of all bacterial cultures accord-ing to teacher directions.

431

Gram’s Staining1. Hold the slide over a beaker, bowl, or

sink.2. Use an eyedropper to cover the smear

with 1 or 2 drops of crystal violet. Wait 30seconds.

3. Wash the slide with distilled water from awash bottle. Do not squirt the waterdirectly on the smear but on the slideabove it.

4. Cover the smear with 1 or 2 drops ofGram’s iodine. Wait 30 seconds.

5. Wash the slide with ethyl alcohol from awash bottle until the alcohol runs clear.

6. Cover the smear with 1 or 2 drops ofsafranin. Wait 30 seconds.

7. Wash the slide with water from a washbottle. Blot dry with microscope tissuepaper.

8. Place the slide on the stage of an oilimmersion microscope. Focus the micro-scope on the lowest setting.

9. Increase the magnification and fine-tunethe focus.

10. Turn the lenses so 2 drops of immersionoil can be placed in the center of the circleon the slide.

11. Turn the 1000x immersion oil lens intoplace. Fine-tune the focus.

12. Sketch the bacteria and record observa-tions. Identify the shape and gram type ofbacteria seen.

13. If time allows, move to other stations toexamine bacteria smears prepared byclassmates.

14. Dispose of petri dishes with bacteria cul-tures and slides according to teacherdirections. Wash all surfaces used with asanitizing solution.

Questions1. What types of bacteria were found?2. Why is it important to wash the slide

after each staining step?3. Why do many doctors’ offices swab

patients’ throats and conduct Gram’sstain tests on the bacteria collected?

4. What can food preparation workers do tohelp reduce contamination of food bybacteria?

list use describe name differentiate identify - g · PDF filethe types of insects present. ... microorganisms work together to spoil food. Softening caused by enzymes can make it easier

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