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Bacteria - Study Notes

1 350 sample was diluted by 10 3 number of bacteria

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Unformatted text preview: iginal sample = 350 x 103 Biological factors Bacteria are effected in growing by nutrients: C, H, N, P, S Temp: low → low speed of enzyme reactions;7 high → denaturisation of enzymes pH → tolerate a wider range of pH than plant and animal cells O2 → some grow better in presence, but some grow in absence Koch's Postulates1 A list of postulates (criteria) must be fulfilled to proof an infective cause for a disease o "Organism must be sufficiently abundant in every case to account for the disease o Organism associated with the disease can be cultivated artificially in pure culture o Cultivated organism produces the disease upon inoculation into another member of the same species o Antibodies to the organism appear during the course of the disease"1 Exceptions are possible o Number of organism causing disease might be very low (eg tuberculosis) o Cultivation might be difficult o Animals must be used as it is unethical to infect a human with a causative organism o Antibodies may not appear if the immune system is inhibited Entry of Microorganisms (Pathogens) into the Body Damaged skin o Skin acts as a barrier to infections o Tetanus occurs when the bacterium Clostridium tetani enters a wound Mucus membrane of respiratory tract o Air containing droplet of infectious material are breathed in o Mycobacterium tuberculosis causes tuberculosis Digestive track o Vibrio cholerae causes cholera when drinking water infected with faeces o Salmonella enteritis causes food poisoning when eating undercooked food o These organisms are resistant to acidic conditions in the stomach o Acid protects against microorganisms by providing a hostile environment Others o Transmission by vectors (e.g. malaria via Plasmodium parasite when mosquito vector takes blood) o Direct entry through the intact skin (e.g. Schistosomiasis where the larval stage schistosome burrows through the skin of the feet)...
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