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BIOS 2150 Class Notes review

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Course
Nursing (BIOS2150)

Institution
Thompson River University (TRU )

. 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. ...

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Uploaded on January 27, 2021
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osmotic pressure
microbiology
bios 2150
temperature considerations

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BIOS 2150 Microbiology Thursday 9/20/18

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

3. Osmotic Pressure (Section 9.5 page 391)
 (Recall the function of the bacterial cell wall from Unit 1) The cell wall
protects the cell from blowing up with an excess of water
 Plasmolysis: loss of water from a cell
o Stop metabolizing due to loss of water. Water loss slows them down.
 High salt and sugar concentration can limit the growth of bacteria
 Fungi can withstand changes in osmotic pressure better than bacterial cells
and typically require less water
o See the theme? Fungi hold up better in more diverse environments
 Hypertonic environments (higher is solutes than inside the cell) cause
plasmolysis due to high osmotic pressure

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