Microbial Growth Control I

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  1. physical
    • temperature
    • temperature and pressure
    • UV radiation
    • filters
  2. chemical
    • disinfectants and antiseptics
    • antibiotics
  3. *sterilization
    killing or removal of all living cells, spores and viruses on an object
  4. disinfection
    • killing or removal of disease-producing organisms from inanimate surfaces
    • pathogens are killed
    • other microbes may survive
  5. antisepsis
    removal of pathogens from surface of living tissue, like skin
  6. sanitation
    reducing the microbial population to safe levels
  7. *D-value
    • decimal reduction time
    • time to kill 90% of cells
  8. heat sterilization
    • death is a function of temperature and time
    • sensitivity of microbe to heat treatment depends on the microbe
  9. Application where D might be used?
    • canning industry
    • pasteurization
  10. How do you actually determine D?
    post-treatment viable cell counts
  11. What is another method of determining the heat sensitivity of an organism?
    thermal death time
  12. Why is autoclave commonly used for heat sterilization?
    • High T achieved using stream under pressure
    • facilitates killing of both vegetative cells and endospores
  13. *pasteurization
    • not sterilization
    • precisely controlled heat to reduce microbial populations
    • prevents spread of pathogens
    • results in reduced spoilage
  14. *UV radiation
    • DNA damage
    • limited to exposed surfaces
    • commonly used in laboratories - decontamination
  15. *ionization radiation
    • sufficient energy to penetrate solids and liquids
    • decontamination/sterilization of medical products and meat products
  16. *filter
    device with pores too small for passage of microorganism but large enough for passage of liquid or gas
  17. *depth filters
    • consists of many pleated layers of a single sheet of treated glass fibers, microbes are trapped in network of fibers
    • remove microorganisms and other particulate contaminants from liquids or air
    • HEPA filter - used in home air filtration
  18. *membrane filters
    • sterilization of heat-sensitive liquids
    • often used in research and clinical laboratories, pharmaceutical industry
  19. chlorine gas and compounds as disinfectants
    reacts with cell membrane and proteins - oxidant
  20. How bleach kills germs
    hypochlorous acid, the active ingredient in bleach, attacks proteins in bacteria, causing them to clump like an egg that has been boiled
  21. triclosan
    • common antiseptic
    • not very soluble in water
    • fat-soluble, easily cross cell membranes
  22. *How would you go about determining the mode of action of triclosan?
    • genetic screen to identify E.coli mutants with increase resistance to triclosan
    • found multiple mutants with point mutation in fabI gene
    • when overexpressed wildtype fabI gene in mutants - recovered sensitivity to triclosan
  23. mechanism of action of antiseptic agent triclosan
    • fabI - enoyl acyl carrier protein reductase involved in fatty acid biosynthesis
    • triclosan blocks fatty acid biosynthesis by targeting fabI - very potent, irreversible inhibitor
    • fatty acid biosynthesis is required for cell membranes - growth is arrested
Card Set:
Microbial Growth Control I
2011-12-08 07:20:18
PMB 112 midterm3

general microbiology midterm 3
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