$$\text{CFU/ml} = \text{number of colonies} \times \text{reciprocal of dilution} \div \text{volume of inoculum}$$

$$35 \times 10^4$ = 350,000$$ CFU/ml

Question 1

Which of the following best describes the physical requirements for microbial growth?

Accepted Answer

Proper temperature, pH, and osmotic pressure

Question 2

A bacterium that grows optimally at temperatures between 25°C and 40°C is classified as:

Accepted Answer

Mesophile

Question 3

Which equation is used to calculate the concentration of bacteria in a sample using the standard plate count method?

Accepted Answer

$$	ext{CFU/ml} = 	ext{number of colonies} 	imes 	ext{reciprocal of dilution} \div 	ext{volume of inoculum}$$

Question 4

Why are obligate anaerobes unable to survive in the presence of oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify oxygen byproducts

Question 5

Which method is best for isolating individual bacterial colonies from a mixed sample?

Accepted Answer

Streak plate method

Question 6

A water sample is filtered and 200 colonies are counted from 100 ml. What is the concentration of bacteria per ml?

Accepted Answer

2 bacteria/ml

Question 7

Which of the following is a chemical requirement for microbial growth?

Accepted Answer

Oxygen

Question 8

What is the primary advantage of using a spectrophotometer to measure bacterial growth?

Accepted Answer

Quick estimation of cell density based on absorbance

Question 9

Which type of bacteria would most likely be found in the Dead Sea, where salt concentration is extremely high?

Accepted Answer

Halophiles

Question 10

During which phase of the bacterial growth curve do cells prepare for division but do not increase in number?

Accepted Answer

Lag phase

Question 11

A culture of E. coli has a generation time of 20 minutes. If you start with 1 cell, how many cells will there be after 2 hours?

Accepted Answer

256

Question 12

Which of the following is NOT a direct method for measuring bacterial growth?

Accepted Answer

Spectrophotometry (turbidity)

Question 13

Which category of bacteria can survive with or without oxygen?

Accepted Answer

Facultative anaerobes

Question 14

What is the role of buffers in culture media?

Accepted Answer

Maintain proper pH for bacterial growth

Question 15

Which of the following best describes a biofilm?

Accepted Answer

A community of microorganisms attached to a surface

Question 16

Which method is most appropriate for isolating anaerobic bacteria?

Accepted Answer

Gas pak jar

Question 17

If a sample is diluted 1:10,000 and 35 colonies are counted on a plate with 1 ml inoculum, what is the concentration of bacteria per ml?

Accepted Answer

$$35 	imes 10^4$ = 350,000$$ CFU/ml

Question 18

Which of the following is a disadvantage of the direct microscopic count method?

Accepted Answer

Cannot distinguish between live and dead cells

Question 19

Which environmental factor is NOT part of 'FATTOM' affecting bacterial growth?

Accepted Answer

Phosphorus

Question 20

What is the significance of a high absorbance value when using a spectrophotometer to measure microbial growth?

Accepted Answer

Indicates a high concentration of cells in the sample

Bacterial Growth: Culture, Requirements, and Measurement

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