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A Simple Guide to Germs and Disease June 2005
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A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

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Page 1: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

A Simple Guide toGerms and Disease

June 2005

Page 2: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Microbiology (1)

Microbiology is the study of organisms not visible to the naked eye, thus requiring the use of a microscope to see them (i.e. microscopic organisms or sometimes called microbes)

Smallest

Largest

Prions

Viruses

Bacteria

Fungi

Protozoa

Page 3: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Microbiology (2)

What are Germs?

• Germs are microorganisms that are likely to cause disease

• Microorganisms are found throughout the environment. Onlya very small number are pathogenic, i.e. capable of causing disease, and not all diseases are caused by microorganisms

• Some bacteria live in our gut and help to digest food.Some yeasts and bacteria are used in baking, brewingor cheese making

• Bacteria are just one type of micro-organism, alongside viruses, fungi and protozoa

Page 4: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

SalmonellaE.coli

Campylobacter

Germs* - Family Tree

*Germs = all potentially harmful micro-organisms

Bacteria Viruses Fungi Protozoa

Germs

GramPositive

GramNegative

SporeFormers

Non-SporeFormers

Bacillus subtilisBacillus cereus

Clostridiumperfringens

StaphylococcusListeria

Enveloped Non-Enveloped

InfluenzaHIv

RotavirusPoliovirus

SRSVMoulds Yeasts

CladosporiumAspergillusPenicillium

Candida

GiardiaCryptosporidium

Page 5: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacteria (1)

Bacteria are prokaryotes and have a characteristic cellular organisation. They are simple, small, unicellular organisms, varying in size between 1-20 um long

Bacteria can be classified by shape:

Spherical (coccus)e.g. Staphylococcus aureus

Rod (bacilli)e.g Escherichia coli

Spiral/helicale.g. Treponema

Page 6: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacteria (2)

• Not all bacteria cause disease. Most bacterial species cannot cause disease. Many even play beneficial roles e.g. producing antibiotics. Our bodies are covered with commensal bacteria (the normal flora)

• Even among bacteria that can cause disease, only a few species are always pathogenic. Many free-living bacteria or members of the normal flora are potentially pathogenic in certain types of individual (particularly the immuno-compromised), but are most of the time harmless

• Consumers tend to be very aware of pathogenic bacteria such as Salmonella, Listeria and E.coli that have made headlines in recent years in connection with outbreaks of food poisoning. They often regard bacteria as modern problems that are more hazardous than traditional “germs”

Page 7: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Classification

The nature of the cell wall determines the classification of bacteria as either Gram-positive or Gram-negative, as determined by the Gram stain

• Gram-positive bacteria: cell wall is a thick multi-layer of peptidoglycan (a mixture of sugars and amino acids)

• Gram-negative bacteria: cell wall is thin and surrounded byan outer membrane (made up of lipopolysaccharides and lipoprotein)

lipoproteinCell wall(peptidoglycan)

Cell membrane(lipid bilayer)

Lipoteichoicacids

Gram-positive Gram-negative

Outermembrane

Page 8: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Growth (1)

Given good growing conditions, a bacterium grows slightly in size or length, new cell wall grows through the centre, and the mother cell splits into two daughter cells. If the environment is optimum, the two daughter cells may split into four in 15-30 minutes. This will continue for some time until the nutrients start to run out or conditions become unstable. Conditions are rarely optimum all of the time.

Page 9: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Growth (2)

Typical Growth Curve for a Bacteria Population• Lag Phase

growth is slow whilst they become used to their new environment and nutrients

• Log Phaseonce the metabolic machinery is running, they start multiplying exponentially, doublingin number every few minutes

• Stationary Phaseas more and more bacteria are competing for nutrients which are decreasing, growth stops and the number of bacteria stabilises

• Death Phasetoxic waste products build up, nutrients have run out and thebacteria begin to die

Page 10: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Growth (3)

and so on ...

Bacteria divideby binary fission

Log

10 v

iable

org

anis

ms/

ml

Time

StationaryLogLag

8.0

6.0

4.0

2.0

0

Death

Time N° of bacteria

0 1

20 mins 2

2 hours 64

6 hours 262,144

8 hours 16,777,216

Typical bacterial growth ratein optimum conditions

Typical growth curvefor a bacteria population

Page 11: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacteria and Temperature

Heat resistanceHIGH

Cl botulinum EBacillus cereus

Cl botulinum A&B

LOW

HIGH

MinimumGrowthTemp.

LOW

Campylobacter

Staph aureusE. coli

Salmonella

Cl perfringens

Listeria

Bacteria die if heatedfor a sufficient time. The longer the time, the greater the destruction

Bacteria stop growing,but do not die4

Bacteria grow quickly

100

63

40

38

36

15

7

0

• Pathogenic bacteria grow best at human body temperature 37ºC. However the majority will grow between 15-45ºC

• Non-sporing cells of bacteria are killed attemperatures above 60ºC. The length of timeranges depending on the organism

• Boiling kills living cells, but will not kill allbacterial spores

• Fridges should be set below 5ºC. Some bacteriasuch as Listeria monocytogenes can growat refrigeration temperatures

Bacteria Grow

at slowerrate

Bacteria grow

Page 12: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Food Poisoning (1)

Because harmful microorganisms are present everywhere in the environment, any food can become contaminated if not properly handled before consumption. There are several causes of food poisoning (bacteria, viruses, parasites, chemicals)

• Infective bacterial food poisoninginfections occur when pathogens are ingested via contaminated food and the bacteria is established in the body, usually growing inside the intestinal tract and irritating intestines e.g. Salmonella spp. and Campylobacter jejuni. The infection may involve subsequent growth in other tissues

• Toxic bacterial food poisoningsome bacteria grow in food and produce a toxin within the foodwhich is then consumed e.g. Bacillus cereus and Staphylococcusaureus. When the food is consumed viable cells of the bacteriado not need to be present. Other microorganisms in food mayproduce harmful or deadly toxins while growing in the intestinaltract e.g. Clostridium perfringens, enterotoxigenic Escherichiacoli and enterohaemorrhagic E. coli

Page 13: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Food Poisoning (2)

The main causes of food poisoning are:

• preparing foods too far in advance

• not cooking foods properly

• storing foods wrongly; so bacteria grow rapidly

• cross contamination of foods after cooking

• infection from people handling foods due to poor hygiene

Page 14: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Food Poisoning (3)

• Campylobacter jejunimost common cause of diarrhoea Sources: raw and undercooked poultry and meat, raw milk and untreated water

• Listeria monocytogenescauses listeriosis, a serious disease for pregnant women,babies, elderly and immunocompromised individuals Sources: dairy products, soft cheeses, raw and undercooked meat, poultry and meat patés

• Salmonella spp.second most common cause of foodborne illness Sources: raw and undercooked eggs,undercooked poultry and meat, dairy products, fruits and vegetables

Page 15: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Bacterial Food Poisoning (4)

• Staphylococcus aureusproduces a toxin that causes vomiting shortly after ingestingSources: cooked foods high in protein e.g. cooked meats, custard, cream cakes

• E. coli O157a bacterium that can produce a deadly toxinSources: undercooked hamburger/ minced beef, contaminated cooked meatand raw milk

• Shigella spp.poor hygiene causes this bacterium to be easily passed from person to personSources: salads, milk and dairy products, and unclean water

Page 16: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Fungi (1)

• Fungi are eukaryotic and exist in different growth forms in different environments. They range from small single cells such as yeasts (~5um) to large complex structuressuch as mushrooms (~5cm)

• The high humidity and temperatures often found in bathrooms and kitchens are conducive to fungal growth. Mould, or mildew as it is sometimes referred, likes warmth and moderateto high humidity

Page 17: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Fungi (2)

Fungi responsible for human disease can be dividedinto two distinct morphological forms

• Yeasts which grow as oval or spherical single cells like bacteria and multiply by budding and division

• Filamentous fungi more commonly known as moulds, consist of long, branching hyphae forming a mycelium. Asexual reproduction results in formation of spores

Page 18: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Fungal Growth

Yeasts - unicellularoval or spherical cells which divide by budding and division

MotherBud formation

Filamentous fungi - branched hyphal structureoften pigmented with age. Reproduce by forming large amountsof spores

Spore MyceliumBranchedhyphae

Daughter

Hyphaldevelopment

Page 19: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Why are fungi a problem?

• They can be responsible for infections• They can cause an allergic response• Fungi cause discolouration and deterioration of household

surfaces giving the characteristic blackening of walls, tile grouting, plaster and around window frames

• Can cause unpleasant odours which are difficult to disguise. Fungi such as Aspergillus, Penicillium, and Alternata have been found to produce volatile organic compounds

• Numerous fungi have been found to produce volatile organic compounds (VOC) and it has been suggested that these affect the health of persons living in mouldy houses. Symptoms include headache, eye, nose and throat irritation and fatigue

• VOC’s have been implicated in health issues relating to sick building syndrome

• Spores of toxigenic fungi contain mycotoxins (toxic secondary metabolites). Many fungal spores are small enough to reach the alveoli in the lungs. The mycotoxins may be transported via the blood from the lung to other body sites, possibly causing other effects e.g. skin lesions

Page 20: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

What infections do fungi cause?

Fungi cause 2 types of infection:

• Superficial mycoses– fungus grows at the body surface in skin, hair and nails

– spread by direct contact, highly contagious and easily spreadto others

• e.g. Candida albicans (thrush and nappy rash)• e.g. dermatophyte fungi: Epidermophyton, Microsporum and

Trichophyton (athlete’s foot)

• Deep mycoses– involve internal organs, usually life-threatening

– rare except in immunocompromised people

– caused by opportunistic fungi (e.g. Aspergillus)

– acquired by inhalation of spores or by entry through wounds

– some part of the normal body flora and are harmless unless the body’s defences are compromised in some way (e.g. Candida)

Page 21: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Fungi are also a source of allergens

• Allergic rhinitis (hayfever)

• Bronchitis

• Asthma

• Extrinsic allergic alveolitis

Almost all microbial allergens are fungal in origin, with the major ones being Penicillium, Aspergillus, Cladosporium and Alternaria

Asthma can be initiated and provoked by allergens commonly encountered in the general environment, for example pollens (trees, grass), house dust mites and moulds, e.g. Alternaria alternata, Cladosporium herbatum and Aspergillus fumigatus

Page 22: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Fungi in the Home

What evidence is there for occurrence of fungal contamination in the home?

There have been a number of studies investigating fungi in the home. Fungi isolated include:

• Penicillium spp.

• Cladosporium spp.

• Aspergillus spp.

• Mycelia sterilia

• Rhodotorula (pink yeasts)

• Sporobolomyces (yeasts)

Fungi isolated from the air was similar in homes surveyed in Scotland, Germany, Finland, North America, Taiwan, Canada and Australia

Page 23: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Viruses

What is a virus? • It is not a bacterium

• It is very small, typically 0.1um

• It is not a true cell

• It is not an independently living organism. It must be insidea living cell to replicate

• They have genetic material but lack cell membranes, cytoplasm and machinery

• The virus uses the infected cell's machinery and enzymes to generate virus parts which are later assembled into new virus particles which leave the cell to infect other cells

• It can infect bacteria, fungi, plants, animals and man

• It may remain viable for long time, even in dry conditions

• It can survive but does not grow in food

Page 24: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

e.g. poliovirusadenovirusrotavirus

Classification based on characteristics such as genetic material present (RNA or DNA), symmetry of virus particle and presence or absence of an envelope

Structurally there are 2 distinct types of virus:Enveloped and Non-EnvelopedNon-enveloped

Structure of Viruses

e.g. herpes simplex

HIVFlu

e.g. hepatitis B

Polymerase

Nucleicacid

Proteincoat

Protein/lipid coatEnvelope

Enveloped

Page 25: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

What infections do viruses cause? (1)

Nearly 1000 different types of viruses are known to infect humans and it has been estimated that they account for approx. 60% of human infections. The young, elderly and immuno-compromised are particularly at risk from virus infections

Many viral diseases are well known and easily identified:

• from colds and flu to chicken pox and measles

• from mumps and herpes to polio, hepatitis and HIV

Page 26: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

What infections do viruses cause? (2)

From the ‘Home Hygiene’ point of view, we are mainly concerned with virus infections relating to poor personal or surface hygiene, and are thus preventable

• Gastrointestinal infections– Gastroenteritis– Diarrhoea– Infectious intestinal disease

• Respiratory infections– Flu– Common cold– Bronchitis

Page 27: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Viruses causing Gastrointestinal Infections

• Rotavirus– Most important viral cause of diarrhoea in children worldwide– Infects virtually all children 3-5 years old in developed and

developing countries– Can be asymptomatic excreter

• Small Round Structured Virus (SRSV) – Play a predominant part in epidemic viral gastroenteritis– Main symptom is projectile vomiting generating aerosols and virus

can be transmitted via aerosols, can contaminate work surfaces with potential for subsequent transfer to food

• Astroviruses and Adenoviruses – Have been associated with gastroenteritis outbreaks in schools,

nursing homes, day-care centres, children’s hospital wards

• Hepatitis A– Viral hepatitis is most common of the food associated virus

diseases,most common vehicle is shellfish

– Easily spread in areas where good personal hygiene is not observed.

– Outbreaks occur in day-care centres, hospitals, nurseries and schools

– Outbreaks may lead to secondary cases in the general community

Page 28: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Viruses causing Respiratory Infections

Viral respiratory infections are common in winter when people are crowded together indoors for longer periods of time, air in ill-ventilated rooms is more humid, favouring survival of suspended enveloped viruses

• Rhinoviruses and coronavirusestogether cause more than 50% of common colds can also cause acute bronchitis

• Influenza virusesmain cause of flu, can cause acute bronchitis

• Parainfluenza virusescause of pneumonia in children

• Respiratory Syncytial Virus (RSV)most important cause of bronchiolitis and pneumonia in infants major cause of hospital-acquired illness on neonatal wards

• Adenoviruscommon cause of sore throats and acute bronchitis

Page 29: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Virus Transmission (1)

Presence or absence of an envelope is the major structural determinant for mode of transmission

• Non-enveloped virusesmost can withstand the acidic environment of the stomachor detergent-like bile of the intestines. Transmitted by respiratory and faecal-oral routes e.g. rotaviruses, SRSV

• Enveloped virusesmore fragile, require an intact envelope for infectivity, sensitive to acids and detergents, so not spread via faecal-oral route; spread in respiratory droplets, blood, saliva. e.g. influenza

Page 30: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Virus Transmission (2)

Activities of the infected host may increasethe efficiency of transmission

• Coughing and sneezing viruses that are better at increasing fluid secretions or irritating respiratory lining will induce more coughing and sneezing increasing efficiency of shedding and transmission

• Diarrhoea eliminates infection more rapidly but is great for contamination of the environment and therefore will spread the microbes

• Projectile vomiting generates aerosols, virus can be transmitted via aerosols, can contaminate work surfaces with potential for subsequent transfer to food

Page 31: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Protozoa (1)

• Protozoa are single-celled eukaryotes

• Live in water or moist places or other organisms as parasites

• Have a resistant transmissable cyst stage

• Transmission to humans via insect bite or accidental ingestion of infective stages

Page 32: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Protozoa (2)

• Cryptosporidium spp. infects the intestines causing Cryptosporidiosis. Large outbreaks are associated with contaminated water or treatment deficiency of water supplies

• Giardia lamblia causes giardiasis, an infection of the small intestine, spread via contaminated food and water and by direct person-to-person contact. Ingestion of one or more cysts may cause disease

• Entamoeba histolyticaan amoeba infecting the large intestine, causes diarrhoea/dysentery, spread via contaminated water or food

• Toxoplasma gondiicauses toxoplasmosis, a very severe disease that can produce central nervous system disorders

Page 33: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Hygiene Hazards In The Home

• Micro-organisms are introduced continually into the home via: people, food, pets, water, insects, air. Wet sites such as sinks, toilets, dishcloths and facecloths can also support microbial growth and themselves become reservoirs of potentially hazardous microorganisms

• Many organisms occurring in the home are of little consequence.Some organisms have the potential to cause infectious disease

• Some people carry highly pathogenic organisms without themselves being affected - other family members unaware of hazard

• Hands, and a whole range of food and hand contact surfaces,combine to provide transfer routes that can move pathogens around the home and ultimately into the body producing infection

Ingestion of:• microorganisms -

bacteria,viruses, protozoa

• toxins - bacterial, fungal

Inhalation of:• toxins

• allergens/spores

• microorganisms

Page 34: A Simple Guide to Germs and Disease June 2005. Microbiology (1) Microbiology is the study of organisms not visible to the naked eye, thus requiring the.

Primary sources SkinInfection

DirectIngestion

FoodPositioning Inhalation

Environment

Air Moulds Mycotoxins

Moulds, viruses,

Legionella,G+bacteria

Water Parasites G-bacteria, Protozoa, viruses

G-bacteria, viruses Legionella

Walls/Ceiling Moulds

Shower/bath/sink

Dermatophytes,

G-bacteriaG-bacteria

Toilet ? G-bacteria, viruses G-/G+bacteria

Kitchen Surface/sink

G-/G+bacteria, Listeria

G-/G+bacteria, Listeria

Furnishing/fabrics

Derm atophytes,

viruses

Dustmites,Moulds

Cleaning aids G-/G+bacteria G-/G+bacteria,

Listeria

Utensils and equipment G-bacteria G-/G+bacteria,

Listeria

People Dermatophytes, viruses

G-bacteria, viruses?

G-bacteria, Staphylococcu

s

G+bacteria,viruses

PetsDermatophytes, Parasites,

virusesG-bacteria Hairfur,

viruses?

InsectParasites, viruses,

G-bacteriaG-bacteria

Rawfood

G-/G+bacteria, Listeria, viruses,

Parasites, mycotoxins

G-/G+bacteria, Listeria

Risk of health hazard from