Question 1

Which of the following best describes a biofilm?

Accepted Answer

A thin, slimy layer that encases bacteria and adheres to a surface, forming an organized community.

Question 2

What is the primary function of quorum sensing in bacterial communities?

Accepted Answer

To coordinate group activities and gene expression based on cell density.

Question 3

A patient develops an infection after a catheter is inserted. Why is a biofilm on the catheter more concerning than free-floating bacteria in the fluid?

Accepted Answer

Biofilms form a protected community attached to the surface, making them harder to eliminate and more likely to cause persistent infection.

Question 4

Which of the following is NOT a requirement for a culture medium to support microbial growth?

Accepted Answer

It must contain a source of light.

Question 5

Why is agar commonly used as a solidifying agent in microbiological media?

Accepted Answer

Few microbes can degrade agar, so it remains solid during microbial growth.

Question 6

Which of the following best distinguishes a chemically defined medium from a complex medium?

Accepted Answer

The exact chemical composition of a chemically defined medium is known.

Question 7

A microbiologist wants to culture an obligate anaerobe. Which of the following methods would be most appropriate?

Accepted Answer

Using a reducing medium containing sodium thioglycolate to remove dissolved oxygen.

Question 8

Which type of culture medium would you use to isolate Salmonella Typhi from a stool sample containing many other bacteria?

Accepted Answer

Selective medium, such as bismuth sulfite agar, which suppresses unwanted microbes.

Question 9

Which of the following best describes the purpose of differential media?

Accepted Answer

To distinguish colonies of the desired organism from other colonies based on visible differences.

Question 10

A microbiologist is trying to detect a rare bacterium in a soil sample. Which type of medium should be used to increase the population of this bacterium to detectable levels?

Accepted Answer

Enrichment medium

Question 11

Which biosafety level (BSL) is required for working with a lethal virus that has no known treatment and requires a sealed, negative-pressure lab with air-supplied suits?

Accepted Answer

BSL-4

Question 12

A bacterium requires elevated levels of CO$$_2$$ for optimal growth. What is the correct term for this type of organism?

Accepted Answer

Capnophile

Question 13

Which of the following scenarios best illustrates the use of both selective and differential media?

Accepted Answer

Mannitol Salt Agar, which allows only salt-tolerant bacteria to grow and distinguishes those that ferment mannitol by a color change.

Question 14

Which of the following is a reason why fastidious bacteria are difficult to culture?

Accepted Answer

They require many specific growth factors that must be supplied in the medium.

Question 15

A laboratory is culturing Mycobacterium leprae, which cannot be grown on artificial media. What special technique should be used?

Accepted Answer

Inoculation into living host cells, such as armadillos.

Question 16

Which of the following best explains why a culture medium must be sterile at the start of an experiment?

Accepted Answer

To ensure that only the intentionally added microbes grow in the culture.

Question 17

Which of the following is a correct sequence for biofilm formation?

Accepted Answer

Microbes reach a surface → cells attach → cells communicate via quorum sensing → community develops

Question 18

Which of the following best describes the main use of reducing media?

Accepted Answer

To support the growth of obligate anaerobes by removing oxygen.

Question 19

A new medium inhibits gram-positive bacteria and all non-Shigella gram-negative bacteria. What type of medium is this?

Accepted Answer

Selective medium

Question 20

Which of the following is NOT a characteristic of complex media?

Accepted Answer

The exact chemical composition is known.

Biofilms & Culture Media: Microbial Communities and Laboratory Growth

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