Question 1

A single bacterium divides every 30 minutes by binary fission. If you start with one bacterium, how many bacteria will there be after 3 hours, assuming no cell death?

Accepted Answer

$$2^{6} = 64$

Question 2

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

Accepted Answer

Log (exponential) phase

Question 3

A microbiologist is studying bacteria that thrive at $$37^{\circ}C$ and are common human pathogens. These bacteria are best classified as:

Accepted Answer

Mesophiles

Question 4

Which enzyme catalyzes the conversion of hydrogen peroxide ($$H_2O_2) $$into water and oxygen, protecting cells from reactive oxygen species?

Accepted Answer

Catalase

Question 5

A bacterium isolated from the Great Salt Lake of Utah is most likely a(n):

Accepted Answer

Halophile

Question 6

Which of the following organisms has no ability to detoxify reactive oxygen species (ROS)?

Accepted Answer

Obligate anaerobe

Question 7

A defined growth medium contains only specific chemical components with known formulas. Which of the following is an example of a defined medium?

Accepted Answer

Medium with $$\mathrm{NaCl}$$, $$\mathrm{$$MgSO_4$$}$$, and glucose

Question 8

Blood agar is used to differentiate bacteria based on their ability to lyse red blood cells. Which type of hemolysis is indicated by a clear, colorless zone around colonies?

Accepted Answer

Beta hemolysis

Question 9

Mannitol salt agar (MSA) is both selective and differential. What does it select for, and what does it differentiate?

Accepted Answer

Selects for halotolerant (salt-tolerant) bacteria; differentiates mannitol fermentation

Question 10

Which of the following is a direct method for counting bacteria?

Accepted Answer

Plate count (colony-forming units)

Question 11

What is the main disadvantage of using turbidity measurements to estimate bacterial numbers?

Accepted Answer

It cannot distinguish between live and dead cells

Question 12

Which process uses heat, steam, and pressure to sterilize microbial media and lab instruments?

Accepted Answer

Autoclaving

Question 13

Boiling water for 5 minutes is effective at killing which of the following?

Accepted Answer

Most bacteria and viruses

Question 14

Which of the following best describes the difference between disinfection and sterilization?

Accepted Answer

Disinfection reduces or eliminates most pathogens; sterilization destroys all forms of microbial life

Question 15

Decimal reduction time ($$D$$ value) is defined as:

Accepted Answer

The time required to reduce a microbial population by 90% at a specific temperature

Question 16

Which chemical agent is most widely used as a halogen disinfectant?

Accepted Answer

Chlorine

Question 17

Alcohols such as ethanol and isopropanol kill microbes primarily by:

Accepted Answer

Denaturing proteins and disrupting cell membranes

Question 18

Which method is most effective for eliminating bacterial endospores?

Accepted Answer

Autoclaving

Question 19

A LifeStraw is a portable water filter that removes microbes from water. What microbial decontamination method does it utilize?

Accepted Answer

Filtration

Question 20

Which two chemical agents are effective at killing Mycobacterium species?

Accepted Answer

Alcohols and phenolics

Question 21

Detergents are described as amphipathic molecules. What does 'amphipathic' mean?

Accepted Answer

They have both hydrophilic and hydrophobic regions

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