Microbial Growth Control I
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- temperature and pressure
- UV radiation
- disinfectants and antiseptics
killing or removal of all living cells, spores and viruses on an object
- killing or removal of disease-producing organisms from inanimate surfaces
- pathogens are killed
- other microbes may survive
removal of pathogens from surface of living tissue, like skin
reducing the microbial population to safe levels
- decimal reduction time
- time to kill 90% of cells
- death is a function of temperature and time
- sensitivity of microbe to heat treatment depends on the microbe
Application where D might be used?
- canning industry
How do you actually determine D?
post-treatment viable cell counts
What is another method of determining the heat sensitivity of an organism?
thermal death time
Why is autoclave commonly used for heat sterilization?
- High T achieved using stream under pressure
- facilitates killing of both vegetative cells and endospores
- not sterilization
- precisely controlled heat to reduce microbial populations
- prevents spread of pathogens
- results in reduced spoilage
- DNA damage
- limited to exposed surfaces
- commonly used in laboratories - decontamination
- sufficient energy to penetrate solids and liquids
- decontamination/sterilization of medical products and meat products
device with pores too small for passage of microorganism but large enough for passage of liquid or gas
- 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
- sterilization of heat-sensitive liquids
- often used in research and clinical laboratories, pharmaceutical industry
chlorine gas and compounds as disinfectants
reacts with cell membrane and proteins - oxidant
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
- common antiseptic
- not very soluble in water
- fat-soluble, easily cross cell membranes
*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
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
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