Question 1

Which phase of bacterial growth in a closed batch system is characterized by a balance between cell division and cell death, resulting in no net increase in cell number? How does this phase differ from growth in a chemostat system?

Accepted Answer

Stationary phase; in a chemostat, cells can be maintained in exponential phase by continuous nutrient supply and waste removal.

Question 2

A bacterium that thrives at pH 2 and is isolated from acidic hot springs is best described as which of the following?

Accepted Answer

Acidophile

Question 3

Which of the following best describes the oxygen requirements and tolerance of a facultative anaerobe?

Accepted Answer

Can grow with or without oxygen, but grows better with oxygen.

Question 4

Superoxide dismutase (SOD) is an enzyme found in many oxygen-tolerant organisms. What is the reaction it catalyzes?

Accepted Answer

$$2O_2^- + 2H^+ \rightarrow O_2$ + H_2O_2$$

Question 5

Which of the following is an example of a differential medium, and what does it allow you to do?

Accepted Answer

MacConkey agar; distinguishes lactose fermenters from non-fermenters by color change.

Question 6

A microbiologist wants to count the number of viable bacteria in a sample. Which method should they use, and why?

Accepted Answer

Spread plate method; it allows counting of only viable cells that can form colonies.

Question 7

Which of the following best defines sterilization?

Accepted Answer

The destruction of all forms of microbial life, including spores.

Question 8

A hospital uses autoclaving to process surgical instruments. Which physical method is being employed, and what is the principle behind its effectiveness?

Accepted Answer

Moist heat under pressure; it denatures proteins and destroys membranes at $$121^\circ C$$ and 15 psi.

Question 9

Which chemical method is most appropriate for disinfecting a surface contaminated with Mycobacterium tuberculosis, and why?

Accepted Answer

Phenolic compounds; they disrupt cell walls and are effective against mycobacteria.

Question 10

When choosing a germicide for use in a hospital, which factor is most critical to consider and why?

Accepted Answer

Spectrum of activity; it must be effective against the expected range of pathogens.

Question 11

Which of the following best describes a psychrophile?

Accepted Answer

An organism that grows optimally at low temperatures, typically below $$15^\circ C.$$

Question 12

A culture medium contains bile salts and crystal violet to inhibit Gram-positive bacteria and lactose with a pH indicator to differentiate lactose fermenters. What type of medium is this?

Accepted Answer

Both selective and differential

Question 13

Which of the following is a correct example of a microaerophile?

Accepted Answer

An organism that requires oxygen at lower than atmospheric concentrations.

Question 14

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

Accepted Answer

Disinfection is used on inanimate objects, while antisepsis is used on living tissue.

Question 15

Which of the following is a correct example of a physical method used for sterilization?

Accepted Answer

Autoclaving

Question 16

A laboratory technician needs to sterilize a heat-sensitive solution. Which method should be used?

Accepted Answer

Filtration

Question 17

Which of the following best describes the action of catalase in aerobic bacteria?

Accepted Answer

It converts $$H_2O_2 to $$water and oxygen, protecting the cell from oxidative damage.

Question 18

Which of the following is a correct example of a heterotroph?

Accepted Answer

A bacterium that obtains carbon from organic compounds.

Question 19

Which of the following is the best example of a chemical agent that can achieve sterilization?

Accepted Answer

Ethylene oxide gas

Question 20

A patient with a wound infection is treated with a germicide. Which factor is most likely to reduce the effectiveness of the germicide?

Accepted Answer

The presence of organic matter such as blood or pus.

Microbial Growth, Adaptation, and Control: Study Notes

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