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Ch. 6 - Microbial Growth
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 6 - Microbial GrowthProblem 6
Chapter 6, Problem 6

A pastry chef accidentally inoculated a cream pie with six S. aureus cells. If S. aureus has a generation time of 60 minutes, how many cells would be in the cream pie after 7 hours?

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1
Identify the initial number of cells, which is given as 6 S. aureus cells.
Determine the total time of growth, which is 7 hours. Convert this time into minutes to match the generation time units: \(7 \text{ hours} \times 60 \text{ minutes/hour} = 420 \text{ minutes}\).
Calculate the number of generations (or cell divisions) that occur during this time by dividing the total time by the generation time: \(\text{number of generations} = \frac{420 \text{ minutes}}{60 \text{ minutes/generation}}\).
Use the formula for bacterial growth to find the final number of cells: \(N = N_0 \times 2^{n}\), where \(N_0\) is the initial number of cells (6), and \(n\) is the number of generations calculated in the previous step.
Substitute the values into the formula and express the final number of cells after 7 hours as \(N = 6 \times 2^{n}\), where \(n\) is the number of generations.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bacterial Generation Time

Generation time is the period required for a bacterial population to double in number. For S. aureus, a generation time of 60 minutes means the population doubles every hour under optimal conditions.
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Generation Times

Binary Fission and Exponential Growth

Bacteria reproduce by binary fission, where one cell divides into two. This leads to exponential growth, meaning the population size doubles at regular intervals, following the formula N = N0 × 2^n.
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Calculating Bacterial Population Over Time

To find the number of cells after a given time, use the initial number of cells (N0), the number of generations (n = total time ÷ generation time), and apply the exponential growth formula. This predicts how many bacteria will be present after growth.
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Related Practice
Textbook Question

Seven methods of measuring microbial growth were explained in this chapter. Categorize each as either a direct or an indirect method.

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Textbook Question

Use the following information to answer questions 1 and 2. Two culture media were inoculated with four different bacteria. After incubation, the following results were obtained:

Medium 2 is:

a. Selective

b. Differential

c. Both selective and differential

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Textbook Question

Which one of the following temperatures would most likely kill a mesophile?

a. -50℃

b. 0℃

c. 9℃

d. 37℃

e. 60℃

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Textbook Question

By deep-freezing, bacteria can be stored without harm for extended periods. Why do refrigeration and freezing preserve foods?

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Textbook Question

Assume you inoculated 100 facultatively anaerobic cells onto nutrient agar and incubated the plate aerobically. You then inoculated 100 cells of the same species onto nutrient agar and incubated the second plate anaerobically. After incubation for 24 hours, you should have

a. more colonies on the aerobic plate.

b. more colonies on the anaerobic plate.

c. the same number of colonies on both plates.

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Textbook Question

The term trace elements refers to

a. The elements CHONPS.

b. Vitamins.

c. Nitrogen, phosphorus, and sulfur.

d. Small mineral requirements.

e. Toxic substances.

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