Q: A bacterial culture is diluted 1:10,000 and 64 colonies are counted on the plate. What is the concentration of bacteria in the original sample?

$$64 \times 10,000 = 640,000$$ cfu/mL

Question 1

Which statement best describes 'microbial growth' as used by microbiologists?

Accepted Answer

It refers to an increase in the number of microbial cells.

Question 2

A food sample stored at 4°C in a refrigerator is most likely to support the growth of which type of microorganism?

Accepted Answer

Psychrotrophs

Question 3

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

Accepted Answer

Carbon

Question 4

A bacterium that can tolerate high salt concentrations but does not require them is classified as:

Accepted Answer

Facultative halophile

Question 5

Which phase of the bacterial growth curve is characterized by exponential increase in cell number?

Accepted Answer

Log phase

Question 6

A colony-forming unit (CFU) is defined as:

Accepted Answer

A single cell or group of attached cells that gives rise to a colony.

Question 7

Which of the following media would you use to selectively grow Gram-negative bacteria while inhibiting Gram-positive bacteria?

Accepted Answer

MacConkey agar

Question 8

Which of the following is NOT a toxic form of oxygen that can cause oxidative damage to cells?

Accepted Answer

Carbon dioxide

Question 9

A bacterial culture is diluted 1:10,000 and 64 colonies are counted on the plate. What is the concentration of bacteria in the original sample?

Accepted Answer

$$64 	imes 10,000 = 640,000$$ cfu/mL

Question 10

Which method is considered an indirect way to estimate bacterial growth in a liquid culture?

Accepted Answer

Turbidity estimation using a spectrophotometer

Question 11

Biofilm formation is primarily driven by which process?

Accepted Answer

Quorum sensing

Question 12

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

Accepted Answer

Osmotic pressure

Question 13

A bacterium that grows best at pH 3 is classified as:

Accepted Answer

Acidophile

Question 14

Which of the following is true about agar?

Accepted Answer

It liquefies at 100°C and solidifies at ~40°C.

Question 15

Which biosafety level (BSL) requires sealed, negative pressure rooms and double filtration of exhaust air?

Accepted Answer

BSL-4

Question 16

During binary fission, which event occurs first?

Accepted Answer

Cell elongation and DNA replication

Question 17

Which of the following is a correct formula for calculating the number of cells after n generations, starting from a single cell?

Accepted Answer

$$2^n$$

Question 18

Which preservation method involves freezing and dehydrating bacteria in a vacuum?

Accepted Answer

Lyophilization

Question 19

Which of the following is a reason why biofilms are more resistant to antibiotics than planktonic bacteria?

Accepted Answer

Biofilms have a shared polysaccharide layer that protects bacteria.

Question 20

A soil sample contains a few phenol-degrading bacteria and thousands of other bacteria. Which culture technique would best allow you to isolate the phenol-degrading bacteria?

Accepted Answer

Enrichment culture using phenol-containing medium

Microbial Growth: Requirements, Biofilms, Culture, and Measurement

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