1. Germs and Disease

2. 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

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

5. 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”

6. 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.

7. 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

8. Fungi (1) Fungi are eukaryotic and exist in different growth forms in different environments. They range from small single cells such as yeasts to large complex structures such as mushrooms. The high humidity and temperatures often found in bathrooms and kitchens are conducive to fungal growth. Mold, or mildew as it is sometimes referred, likes warmth and moderate to high humidity.

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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