Lecture 6-Microbial control colored

Lecture 6-Microbial control colored - Control of...

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1 Control of Microorganisms Bio3124 Lecture #6 Definitions ± sterilization destruction /removal of all viable organisms ± disinfection killing, inhibition, removal of pathogens disinfectants usually chemical used on inanimate objects ± sanitization reduction of microbial population to levels deemed safe ± antisepsis prevention of infection of living tissue by microorganisms ± antiseptics chemical agents, kill or inhibit growth of microorganisms when applied to tissues ± Chemotherapy: internal use chemicals to kill or inhibit microbes within host tissues Definitions… ± Antimicrobials: ± -cidal agents: agent kills, commonly called germicides ± kills pathogens and many nonpathogens but not necessarily endospores ± include bactericides, fungicides, algicides, and virucides ± -static agents: agent inhibits growth ± include bacteriostatic and fungistatic
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2 Microbial Death ± microorganisms are not killed instantly ± death curves are 100 120 1E+09 1E+10 1E+11 Bacterial Death Curve l) /ml) exponential ± Plot: log of survivors vs antimicrobial exposure time ± The slope: average death rate 0 20 40 60 80 1234567891 01 11 2 1 10 100 1000 10000 100000 1E+06 1E+07 1E+08 Survivorsx10 9 (CFU/m Survivors( log of CFU/ Time Effectiveness of Antimicrobial Agent Activity Depends on: ± population size ± population composition vegetative vs dormant ± concentration ± duration of exposure longer exposure more organisms killed ± temperature higher temperatures usually increase killing ± local environment e.g., pH, viscosity and concentration of organic matter organisms in biofilms are physiologically altered and less susceptible to many antimicrobial agents Methods in controlling microorganisms Two major methods are used, ± Physical methods ± Heat ± Moist heat sterilization (autoclaves) ± Pasteurization ± Dry heat sterilization (ovens, incinerators) ± Low temperature (refrigeration, freezing) ± Filtration (for heat labile liquids) ± Irradiation (UV and ionizing radiation) ± Chemical methods ± Disinfectants and antiseptics (phenolics,alcohols, aldehydes, gases… etc) ± Chemotherapeutic agents (internal use)
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3 Moist Heat Sterilization ± above 100 o C , requires saturated steam under pressure ( autoclave ) ± effective against all types of microorganisms and spores ± degrades nucleic acids, denatures proteins, and disrupts membranes ± Autoclave ² 121°C, 15 psi (2 atm) for 20 minutes The Autoclave or Steam Sterilizer ² Kills all bacteria ² Kills endospores ± Clostridium botulinum 9 Botulism ± Bacillus anthracis – Anthrax Pasteurization ± Louis Pasteur and Claude Bernard (1862) ± does not sterilize ± logarithmic reduction of germs rather than killing them all ± Most often ~5 log reduction; milk, beer, apple cider, fruit juice and other beverages
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Lecture 6-Microbial control colored - Control of...

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