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summaries2.pdf - Megan Jaros Rod Allrich Animal Health...

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Megan Jaros Rod Allrich Animal Health Management 27 September 2017 Summary #1: 70% ETOH Bacteria can cause death and disease in humans. Therefore, disinfectants are necessary to kill or eliminate bacteria, especially in a laboratory setting. The most common disinfectants used in labs are ethanol, anti-bacterial hand soap, and bleach. There are 5 different disinfectant categories: alkylating, sulfhydryl combining, oxidizing, dehydrating, and permeable. Bleach, an oxidizing disinfectant, attacks lipids, proteins, and DNA in microorganisms. The cellular components are essential to survival of the microorganisms, thereby killing it. Ethanol, a dehydrating disinfectant, rapidly denatures the cellular membrane, causing it to lyse (burst). Hand soap strips away the outer layer of oil on the skin. This prevents bacteria from coming to the surface of the hand. This article details an experiment where the efficiency of these three disinfectants (10% commercial bleach, 70% laboratory ethanol, and 50% commercial anti-bacterial hand soap) was tested against E. Coli. Four different contact times (30 seconds, 1 minute, 5 minutes, and 10 minutes) were also tested. Also, two different E. Coli strains were tested; one was isolated from a pure sample supplied by a bioresource company while the other was a mixed sample collected from “aerobic sludge” in an experimental laboratory. Spread plating was done to determine the initial cell concentration, then both samples were incubated for 24 hours at 37˚C. The experiment took place in 1.5mL tubes. 0.1mL of the chosen E. Coli culture was added to 0.9mL of the chosen disinfectant for the chosen time. After the indicated time was up, the tube was centrifuged and the supernatant was discarded. The tube was refilled with deionized water, spread plated, and incubated at 37˚C for 24 hours. The next day, the number of colonies were counted to determine bacteria concentration and compared to the initial cell concentration data to get the colony reduction rate. For both the mixed and pure culture, bleach has the best efficiency for all of the time intervals except for the 5-minute pure culture (for which ethanol is slightly more effective). Bleach has the best efficiency because the plates with bleach have the lowest number of colonies, with reduction rates generally above 99.99%. Ethanol was a close second to bleach, with reduction rates generally above 99.90%. Hand soap preformed extremely poorly; all of the samples at all times had very similar concentrations to the initial cell concentrations. The data also shows that ethanol has a higher reduction rate for pure E. Coli as opposed to mixed E. Coli and that time plays a bigger role in the mixed E. Coli sample compared to the pure sample. Hand soap had comparable reduction rates to water as a disinfectant, suggesting that hand soap may have a delayed reaction while bleach and ethanol are immediately effective. Overall, bleach is the most effective sterilization method followed closely by ethanol. Hand soap, on the other hand, is not an ideal disinfectant and is not an effective method to kill bacteria. However, different types of bacteria have different properties. Because of this, what works for E. Coli may not work for a different
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