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Lecture 16

MBIO 1010 Lecture 16: Lecture 16

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MBIO 1010
Christopher Rathgeber

Microbiology 1010 – Lecture Notes General Principles and Growth Control by Heat (Continued…) The autoclave is a sealed device that uses steam under pressure (Figure  5.33) o Allows temperature of water to get above 100ºC o It's not the pressure, but the high temperature in a moist environment, that kills the microbes  o  o 121 C for 15 min (15 pounds per square inch of pressure), is typically used. o To ensure sterility this means that the point that takes the longest to heat must stay at 121 for 15 min. Autoclave – the gold standard Moist heat is more effective 15psi = increases pressure which increases the pressure on the water molecules which keeps the hydrogen bonds attached on the oxygen so it stays in the liquid form. Destroys endospores, viruses etc. 89 Microbiology 1010 – Lecture Notes Other Physical Control Methods: Radiation and Filtration Microwaves, UV, X-rays, gamma rays, and electrons can reduce microbial growth  UV has sufficient energy to cause modifications and breaks in DNA o UV is useful for decontaminating surfaces Cannot penetrate solid, opaque, or light-absorbing surfaces Ionizing radiation  Electromagnetic radiation that produces ions and other reactive molecules generates electrons, hydroxyl radicals, and hydride radicals. Some microorganisms are more resistant to radiation than others. Amount of energy required to reduce viability tenfold is analogous to D value Other Physical Control Methods: Radiation and Filtration (Continued…) Sources of radiation include cathode ray tubes, X-rays, and radioactive nuclides  Radiation is used for sterilization in the medical field and food industry  Radiation is approved by the WHO and is used in the USA for decontaminating foods particularly susceptible to microbial contamination Hamburger, chicken, spices may all be irradiated Other Physical Control Methods: Radiation and Filtration (Continued…) Filtration avoids the use of heat on sensitive liquids and gases o Pores of filter are too small for organisms to pass through o Pores allow liquid or gas to pass through o Examples include HEPA filters and membrane filters o With membrane filters, filtration can be accomplished by syringe, pump, or vacuum. 90 Microbiology 1010 – Lecture Notes a) Pore size is 5 µm. Note the size of the pores relative to the size of some of the bacteria. Is this an appropriate filter to prevent bacteria from going through? a) Pore size 0.2 µm.  Note the pore size relative to Leptospira (0.1 x 20 µm)  This filter prevents most bacteria from going through. Pore size 0.2 µm = Nice size. As a result, I can trap the bacteria more effectively. Too small of size, can still go through the trap and can go into the solution. Chemical Control of
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