1. A Simple Guide to Germs and Disease
June 2005

2. Microbiology (1) Smallest Largest
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
Prions
Viruses
Bacteria
Fungi
Protozoa
Largest

3. Microbiology (2) What are Germs?
Germs are microorganisms that are likely to cause disease
Microorganisms are found throughout the environment. Only a 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, brewing or cheese making
Bacteria are just one type of micro-organism, alongside viruses, fungi and protozoa

4. Clostridium perfringens
Germs* - Family Tree
Germs
Bacteria
Viruses
Fungi
Protozoa
Gram Positive
Gram Negative
Enveloped
Non- Enveloped
Giardia
Cryptosporidium
Spore Formers
Non-Spore Formers
Influenza
HIv
Rotavirus
Poliovirus
SRSV
Moulds
Yeasts
Salmonella
E.coli
Campylobacter
Bacillus subtilis
Bacillus cereus
Clostridium perfringens
Staphylococcus
Listeria
Cladosporium
Aspergillus
Penicillium
Candida
*Germs = all potentially harmful micro-organisms

5. e.g. Staphylococcus aureus
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
Spiral/helical
e.g. Treponema
Rod (bacilli)
e.g Escherichia coli

6. 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”

7. 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 by an outer membrane (made up of lipopolysaccharides and lipoprotein)
Lipoteichoic acids
Outer membrane
Cell wall
(peptidoglycan)
lipoprotein
Cell membrane
(lipid bilayer)
Gram-positive
Gram-negative

8. 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 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.

9. 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 Phase once the metabolic machinery is running, they start multiplying exponentially, doublingin number every few minutes
Stationary Phase as more and more bacteria are competing for nutrients which are decreasing, growth stops and the number of bacteria stabilises
Death Phase toxic waste products build up, nutrients have run out and thebacteria begin to die

10. Bacterial Growth (3)
Typical bacterial growth rate in optimum conditions
Bacteria divide by binary fission
Time
N° of bacteria 1
20 mins 2
2 hours 64
6 hours
262,144
8 hours
16,777,216
Typical growth curve for a bacteria population
8.0
6.0
Log10 viable organisms/ml
4.0
and so on ...
2.0
Lag
Log
Stationary
Death
Time

11. Bacteria and Temperature
HIGH
100
Campylobacter
Cl botulinum A&B
Bacteria die if heated for a sufficient time.
The longer the time, the greater the destruction
Minimum Growth Temp.
Staph aureus
E. coli
Salmonella
Cl perfringens
Cl botulinum E
Bacillus cereus 63
Listeria
LOW 40 38
LOW
HIGH
Heat resistance
Bacteria
grow
Bacteria
Grow
at slower
rate
Bacteria grow
quickly
Pathogenic bacteria grow best at human body temperature 37ºC. However the majority will grow between 15-45ºC
Non-sporing cells of bacteria are killed at temperatures above 60ºC. The length of time ranges depending on the organism
Boiling kills living cells, but will not kill all bacterial spores
Fridges should be set below 5ºC. Some bacteria such as Listeria monocytogenes can grow at refrigeration temperatures 36 15 7
Bacteria stop growing,
but do not die 4

12. 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 poisoning infections 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 poisoning some bacteria grow in food and produce a toxin within the food which is then consumed e.g. Bacillus cereus and Staphylococcus aureus. When the food is consumed viable cells of the bacteria do not need to be present. Other microorganisms in food may produce harmful or deadly toxins while growing in the intestinal tract e.g. Clostridium perfringens, enterotoxigenic Escherichia coli and enterohaemorrhagic E. coli

13. 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

14. Bacterial Food Poisoning (3)
Campylobacter jejuni most common cause of diarrhoea Sources: raw and undercooked poultry and meat, raw milk and untreated water
Listeria monocytogenes causes 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

15. Bacterial Food Poisoning (4)
Staphylococcus aureus produces a toxin that causes vomiting shortly after ingesting Sources: cooked foods high in protein e.g. cooked meats, custard, cream cakes
E. coli O157 a bacterium that can produce a deadly toxin Sources: undercooked hamburger/ minced beef, contaminated cooked meat and raw milk
Shigella spp. poor hygiene causes this bacterium to be easily passed from person to person Sources: salads, milk and dairy products, and unclean water

16. 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 structures such 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 moderate to high humidity

17. Fungi (2)
Fungi responsible for human disease can be divided into 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

18. Fungal Growth
Bud formation
Mother
Daughter
Yeasts - unicellular oval or spherical cells which divide by budding and division
Spore
Hyphal development
Branched
hyphae
Mycelium
Filamentous fungi - branched hyphal structure
often pigmented with age. Reproduce by forming large amounts of spores

19. 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

20. 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 spread to 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)

21. 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

22. 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

23. 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 inside a 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

24. Structure of Viruses Non-enveloped Enveloped
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-Enveloped
Non-enveloped
Enveloped
Protein/lipid coat
Envelope
Protein coat
Nucleic acid
Polymerase
e.g. poliovirus adenovirus rotavirus
e.g. hepatitis B
e.g. herpes simplex
HIV
Flu

25. 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

26. 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

27. 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

28. 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 coronaviruses together cause more than 50% of common colds can also cause acute bronchitis
Influenza viruses main cause of flu, can cause acute bronchitis
Parainfluenza viruses cause 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
Adenovirus common cause of sore throats and acute bronchitis

29. Virus Transmission (1)
Presence or absence of an envelope is the major structural determinant for mode of transmission
Non-enveloped viruses most can withstand the acidic environment of the stomach or detergent-like bile of the intestines. Transmitted by respiratory and faecal-oral routes e.g. rotaviruses, SRSV
Enveloped viruses more 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

30. Virus Transmission (2)
Activities of the infected host may increase the 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

31. 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

32. 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 histolytica an amoeba infecting the large intestine, causes diarrhoea/dysentery, spread via contaminated water or food
Toxoplasma gondii causes toxoplasmosis, a very severe disease that can produce central nervous system disorders

33. 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

34. Risk of health hazard from
Primary sources
Skin Infection
Direct Ingestion
Food Positioning
Inhalation
Environment
Air
Moulds
Mycotoxins
Moulds, viruses, Legionella, G+bacteria
Water
Parasites
G-bacteria, Protozoa, viruses
G-bacteria, viruses
Legionella
Walls/Ceiling
Shower/bath/sink
Dermatophytes, G-bacteria
G-bacteria
Toilet ?
G-bacteria, viruses
G-/G+bacteria
Kitchen Surface/sink
G-/G+bacteria, Listeria
Furnishing/fabrics
Derm atophytes, viruses
Dustmites, Moulds
Cleaning aids
Utensils and equipment
People
Dermatophytes, viruses
G-bacteria, viruses?
G-bacteria, Staphylococcus
G+bacteria, viruses
Pets
Dermatophytes, Parasites, viruses
Hairfur, viruses?
Insect
Parasites, viruses, G-bacteria
Rawfood
G-/G+bacteria, Listeria, viruses, Parasites, mycotoxins