Question 1

Which of the following best describes the difference between planktonic and biofilm growth in bacteria?

Accepted Answer

Planktonic growth refers to free-floating bacterial cells, while biofilm growth involves bacteria attached to surfaces and embedded in a matrix.

Question 2

A batch culture of bacteria is observed to have no increase in cell number for several hours after inoculation. Which phase of growth is this, and what is occurring at the cellular level?

Accepted Answer

Lag phase; cells are adjusting to the new environment and preparing for division.

Question 3

Which of the following statements about the chemostat is correct?

Accepted Answer

A chemostat maintains bacterial cultures in exponential phase by continuously adding fresh medium and removing waste.

Question 4

A microbiologist wants to estimate the number of viable bacteria in a milk sample. She performs a serial dilution to $$10^6$$ and plates $$0.1 mL of $$the final dilution, obtaining 25 colonies. What is the estimated concentration of bacteria in the original sample (in CFU/mL)?

Accepted Answer

$$2.5 	imes 10^7$ CFU/mL

Question 5

Which of the following best explains why endospores are not killed by boiling for 20 minutes?

Accepted Answer

Endospores have a thick protein coat and dehydrated core that protect them from heat.

Question 6

A hospital is deciding how to disinfect a surgical instrument that will contact sterile body tissues. Which level of germicide and method should be used?

Accepted Answer

High-level germicide or sterilization, such as autoclaving.

Question 7

Which of the following best describes the function of superoxide dismutase and catalase in aerobic bacteria?

Accepted Answer

They are enzymes that detoxify reactive oxygen species, allowing survival in oxygen-rich environments.

Question 8

Which type of laboratory medium would you use to distinguish between bacteria that ferment lactose and those that do not, and why?

Accepted Answer

Differential medium, because it contains indicators that reveal differences in lactose fermentation.

Question 9

A bacterium is classified as a mesophile. Which of the following environments would most likely support its optimal growth?

Accepted Answer

A human body at $$37^\circC$$

Question 10

Which of the following best describes the purpose of the streak plate technique in microbiology?

Accepted Answer

To isolate individual colonies from a mixed bacterial sample.

Question 11

A microbiologist is working with a bacterium that cannot synthesize certain vitamins and must obtain them from the environment. What is the term for these required organic molecules?

Accepted Answer

Growth factors

Question 12

Which of the following statements about autoclaving is correct?

Accepted Answer

Autoclaving uses pressurized steam at $$121^\circC to $$achieve sterilization.

Question 13

Which of the following best explains why buffers are added to microbial growth media?

Accepted Answer

To maintain a stable pH and prevent acidification from metabolic byproducts.

Question 14

A sample is filtered through a membrane with a pore size of $$0.1\ \mu m. $$Which of the following is true regarding the outcome?

Accepted Answer

All bacteria will be removed, but some viruses may pass through.

Question 15

Which of the following is a correct application of the decimal reduction time ($$D$$ value) in microbial control?

Accepted Answer

It is the time required to reduce a microbial population by 90% at a specific temperature.

Question 16

Which of the following best describes the action of non-ionizing radiation (such as UV light) on microbial cells?

Accepted Answer

It produces thymine dimers in DNA, leading to mutations and cell death.

Question 17

A laboratory technician is using MacConkey agar to culture bacteria from a stool sample. What is the primary function of this medium?

Accepted Answer

It is a selective and differential medium that inhibits Gram-positive bacteria and distinguishes lactose fermenters.

Question 18

Which of the following is a correct example of a physical method of microbial control and its application?

Accepted Answer

Using UV light to disinfect surfaces in a biosafety cabinet.

Question 19

A patient with a wound infection is treated with a topical antiseptic. Which of the following statements best describes an antiseptic?

Accepted Answer

A chemical applied to living tissue to reduce microbial numbers.

Question 20

Which of the following best explains why some bacteria are classified as obligate anaerobes?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase, making oxygen toxic to them.

Microbial Growth: Principles, Laboratory Methods, and Control

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