. 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.
...
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
1
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller Welch1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $4.49. You're not tied to anything after your purchase.
