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lecture16 - 20.106J Systems Microbiology Lecture 16 Prof...

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20.106J – Systems Microbiology Lecture 16 Prof. Schauer ¾ Chapter 20 ± Microbial growth control o Physical antimicrobial control o Chemicals that are used externally o Antimicrobial agents used internally o Antimicrobial drug resistance and discovery of new drugs ± Physical antimicrobial control o Anything that you’d expect is injurious to your cells is likely injurious to bacterial cells as well o Heat – the most common means of controlling bacterial populations o Radiation o Filtration – removes the bacteria, rather than killing them ± Heat o Measuring heat sterilization ± Graph: survival fraction vs. time ± Death time (10-fold reduction at a given temperature) ± Thermal death time – easier to determine o Autoclave ± Steam at very high pressures – a giant pressure cooker ± Steam at 121 degrees Celsius ± Sterilizes things that can survive that high temperature ± If you’re sterilizing something very large, like a large vat of liquid, it’s difficult for the steam to penetrate ± If you’re autoclaving something like surgical instruments, you wrap them in a porous material first, so that microbes don’t get back onto them after they’re autoclaved o Pasteurization ± At the time that this was invented at the turn of the last century, there were huge problems with pathogens transmitted through milk, such as tuberculosis ± You need to very carefully control both the absolute temperature and the flow of the milk through the machine ± Flash pasteurization is 71 degrees Celsius for 15 seconds ± There is always the possibility today of picking up pathogens like Listeria, Salmonella, and E. coli if you consume non-pasteurized dairy ± Radiation Sterilization o UV can’t penetrate anything that isn’t transparent
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o It’s useful for control of surfaces o Sometimes it’s useful to sterilize water o It’s difficult to achieve complete sterilization with UV
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lecture16 - 20.106J Systems Microbiology Lecture 16 Prof...

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