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:
...
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
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