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BIOS2150: Microbiology Exam study guide

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1. Temperature (Section 9.4) • Psychrophiles: prefer cooler temperatures (below 15 degrees C). Do not live in humans. (Psychorotrophs grow at higher temps and can cause spoilage of refrigerated ... foods). • Mesophiles: prefer 25-40 degrees C. Live in humans as pathogens and non-pathogens. • Thermophiles: prefer 50-60 degrees C. Found in compost piles and hot springs. o Often domain archaea o Often not pathogens to humans Temperature Considerations: • Minimum growth temperature o Doesn’t necessarily kill them… they just stop metabolizing • Should your refrigerator be set above or below this temperature? Below 40. • Optimum growth temperature o Where they are going to do best. Human pathogens typically like 37 degree Celcius • Maximum growth temperature o The highest they can withstand o As you get closer to the minimum and maximum the growth slows • Should buffet food lines hold food above or below this temperature? Above. 2. pH (Section 9.3) • Most bacteria prefer a pH that is near neutral (6.5-7.5) o pH is a measure of the hydrogen ion (H+) concentration o Scale runs from 0-14. At 7 it is a one-to-one ratio. H+OH-  As you go down the scale there is a excess of H+  Up the scale you have an excess of OH- o Hydrogen ions binds to bacterial enzymes and cause them to fail (preventing the bacteria from metabolizing) • Fungi can tolerate more acidic conditions • Microbes called Acidophiles grow in acidic environments [Show More]

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