Microbiology Critical Thinking Day Three
Answer critical Thinking question #2 for chapter 6 on page 180.
Answers should be submitted in word document with any associated
references used
1 E.Coli was incubated with aeration in a nutrient medium
containing two carbon sources, and the following growth curve was
made from this culture
A) Explain what happened at the time marked x
B) Which substrate provided “better” growth condition for the
bacteria? How can you tell?
2 Assume that after washing your hands you leave ten
bacterial cells on a new bar of soap. You then decided to do a
plate count of a soap after it was left in soap dish for 24 hours.
You dilute one gram of the soap 1:106 and plate it on heterotrophic
plate count agar. After 24 hours of incubation, there are 168
colonies. How many bacterial were on the soap? How did they get
there?
3) Heat lamps are commonly used to maintain food at about 50
degree C for as long as 12 hours in cafeteria serving lines . The
following experiment was conducted to determine whether this
practice poses a potential health hazard.
Beef cubes were surface-inoculated with 500,000 bacterial
cells and incubated at 43-53degree C to establish temperature
limits for bacterial growth. The following results were obtained
from heterotrophic plate counts performed on beef cubes at 6 and 12
hours after incubation.
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