Assignment

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.