Food Biotechnology Dr. Kamal E. M. Elkahlout Food Microbiology 2 Microbial Food-Borne Diseases.

Food BiotechnologyDr. Kamal E. M. Elkahlout

Food Microbiology 2Microbial Food-Borne Diseases

Types of microbial food-borne diseases

• Intoxication• illness occurs as a consequence of ingestion of a

preformed bacterial or mold toxin (mycotoxin) due to its growth in a food.

• A toxin has to be present in the contaminated food in an active form.

• Once the microorganisms have grown and produced toxin in the food, there is no need of viable cells during the consumption of the food for illness to occur.

• Eg. Staphylococcal food poisoning.

Infection• Illness results from consumption of food and water

contaminated with entero-pathogenic bacteria or viruses.

• It is necessary for entero-pathogenic bacteria and viruses to remain alive in the food or water during consumption.

• viable cells present in small numbers have the potential to establish and multiply in the digestive tract to cause the illness.

• Eg. Salmonellosis, Hepatitis A.

Toxico-infection• Illness results from ingestion of a large number of

viable cells of some pathogenic bacteria through contaminated food and water.

• The bacterial cells either sporulate or die and release toxin(s) to produce the symptoms.

• Eg. C. perifringens gastroenteritis

Food intoxications• Toxin is produced by a pathogen while growing in a food. • Toxin can be heat labile or heat stable.• Ingestion of a food containing active toxin, not viable

microbial cells, is necessary for poisoning.• Symptoms generally occur quickly, as early as 30 min

after ingestions• Febrile symptom is not present• Symptoms differ with type of toxin:• Enterotoxins produce gastric symptoms. • Neurotoxins produce neurological symptoms

Staphylococcus aureus

• Organism• Are Gram positive cocci• Occur generally in grape like clusters• Are nonmotile, noncapsular

and nonsporulating

Growth• Are facultative anaerobes but grow rapidly under aerobic

conditions.• Cells are killed at 66°C in 12 min and at 72°C in 15s.• They are mesophiles with a growth range between 7-48°C and a

rapid growth between 20-37°C.• They can ferment CHOs and also cause proteolysis by the

extracellular proteolytic enzymes.• Grows well at low Aw (0.86), low pH (4.8) and high salt and sugar

concentrations at 15% and in the presence of NO2.• Able to grow under several adverse conditions, Sta. aureus can

grow in many foods.• Poor competitors in the presence of many other microorganisms

in foods.• Enterotoxin-producing Sta. aureus strains associated with

staphylococcal food intoxication.

Habitat• Sta. aureus naturally present in the nose, throat,

skin and hair (feathers) of healthy humans, animals and birds.

• Can be present in infections such as cuts in the skin and abscesses in humans, animals and birds, cuts in hands and facial erupted acne in humans.

Toxin and toxin production• 6 enterotoxins are produced by enterotoxigenic strains:-

A, B, C1, C2, D and E (also known as SEA, etc) • The toxins vary in heat stability (SEB more stable than

SEA) • Normal temp and time used in processing or

conventional heating will not destroy the potency of the toxins.

• Rate of toxin production by a strain is directly related to its rate of growth and cell conc. Optimum growth occurs around 37-40°C.

• Staphylococcal toxins are enteric toxins and cause gasteroenteritis.

Disease and symptoms• Symptoms occur within 2-4h with a range of

30min-8h and are directly related to the potency and the amounts of toxin ingested and an individuals resistance.

• - Primary symptoms - salivation, nausea, & vomitting, abdominal cramps & diarrhea

• - Secondary symptoms - sweating, chills, headache & dehydration

Botulism• Results in consumption of food containing toxin of

Clostridium botulinum.• Is a Neurotoxin and produces neurological

symptoms along with some gastric symptoms• Infant botulism occurs from the ingestion by the

infant of C. botulinum spores that germinate, grow and produce toxins in the GI tranct and cause specific symptoms.

Organism• Cells are gram positive rods• Occur as single cells or in small chains, many are

motile• Obligate anaerobes and form single terminal spores• Cells are sensitive to low pH (<4.6) , low Aw

moderate high salt(5.5%).• Spores do not germinate in presence of nitrate

(250ppm).• Spores are highly resistant to heat (killed at 115°C).• Cells are killed at moderate temp (pasteurization).• Strains are proteolytic and nonproteolytic

Growth• Strains (type of toxin production) divided into 6 types -

A, B, C, D, E and F• A, B, E and F - associated with human foodborne

intoxications• A- proteolytic, E-nonproteolytic• B & F either proteolytic or nonproteolytic.• Proteolytic strains - grow b/w 10°C and about 48°C with

optimum temp of 35°C• Nonproteolytic strains - grow in the range of 3.3-45°C,

optimum at 30°C• For growth - anaerobic condition

Habitat• Spores of C. botulinum are widely distributed in soil,

sewage, mud, sediments of marshes, lakes and coastal waters, plants, and intestinal contents of animals and fishes.

• Fruits and vegetables can be contaminated with spores from soil.

• Fishes from water and sediments• Types A and B spores are more prevalent in soil,

sewage and fecal matters of animals• Type E spores are generally found in marine

environment.

Toxins and disease and symptoms• Toxins are neurotoxic proteins• For food intoxication in humans - Type A, B, E and F -

extremely potent• Following ingestion• Toxins absorbed through intestinal wall, spread to the

nerves and they block the transmission of impulse.• At initial stage (12-36h, but can be 2h) some GI

disorders (nausea, vomiting, diarrhoea and constipation) may be evident.

• Neorological symptoms develop within a short time, esp if amount consumed is high.

• Highly potent toxins-(1ng/kg body weight) is necessary for severe symptoms and even death.

• Neurological symptoms include difficulty in breathing, speaking, dryness of mouth, paralyses in all involuntary muscles that spreads to the diaphragm, lungs and heart.

• Death usually results from respiratory failure.• Toxins are antigenic (contains antigen) - thus

antitoxins are present

Botullism Poisoning• Source of trouble:• Low acid foods that were improper

canned• Trouble signs• Clear liquid turn milky• Cracked jars• Loose or dented lids• Swollen or dented cans• An off odor

• Prevention• Examine all canned foods before cooking• Cook & reheat foods thoroughly• Keep cooked food hot above 140 degrees or

cold below 40 degrees.• Symptoms after eating• Double vision and droopy eyelids• Trouble speaking, swallowing or breathing• Untreated botullism can be fatal.

MYCTOXICOSIS• Organism• Toxigenic species and strains of molds from meany genera

are known to produce mycotoxins• Some toxigenic strains from several species and genera

and the toxin they produce include:• - Asp. flavus (alfatoxin)• - Asp. parasiticus (alfatoxin)• - Asp. nidulans (sterigmatocystin)• - Penicillium viridicatum (ochratoxin)• - Pen. patulum (patulin)• - Pen. roqueforti (roquefortin)• The toxigenic strains cannot be differentiated from

nontoxigenic strains.

Growth

• Molds grow best in humid and warm environments.• They are aerobic and thus need air for growth• they can grow slowly at very low Aw (0.65), low

temperature (refrigerated temp) and low pH (3.5)• These conditions are often used to extend the shelf

life of many foods.• Unless vacuum packaging is used, molds can grow

in foods and if toxigenic can produce toxins in foods.

Habitat

• Spores are present in • - Soil• - Dust• - environment• Many foods have viable spores or mycelia

especially before heat treatment.

Toxin and toxin production• Mycotoxins include a large numbers of toxins

produced by different toxigenic species and strains of molds.

• Are small molecular hetrocyclic organic compounds and have more than one chemicial type. E.g aflatoxin (B1 and G1).

• Produced by the toxigenic mold strains as secondary metabolites.

• Toxin production in general is directly related to the growth rate of a mold strain

Food association• Consumption of mycotoxin-contaminated food can

cause mycotoxicosis in humans.• Feeding moldy products to food animals and birds

can also produce foods of animal origin (milk , eggs) that are contaminated with mycotoxins.

• Many of the mycotoxins are resistant to heat used in the normal preparation of foods.

Prevention of micotoxicosis• contamination of food with toxigenic mold strains

(or all molds) should be reduced.• Proper packaging should be used to reduce the

incidence.• Heat treatment where applicable reduce load by

killing molds and their spores.• Preventing growth in food and in feeds.• Use anaerobic packaging.

• Reduce Aw where possible to ≤ 0.6• Freezing• Using specific preservatives against mold growth.• Chemical treatments-ammonia, hydrogen peroxide

and sodium hypochlorite inactivates alfatoxins.• Trimming -not a good methods as the remaining

portion may have some mycotoxins.