$$\text{Chemically defined medium} = \text{Water} + \text{Exact amounts of carbon, nitrogen, energy, minerals}$$

Question 1

Which of the following best describes why agar is preferred over gelatin as a solidifying agent in bacterial culture media?

Accepted Answer

Agar does not melt easily and is not digested by most bacteria, making it ideal for solid media.

Question 2

A scientist wants to isolate Mycobacterium tuberculosis from a patient sample. Which culture medium should be used and why?

Accepted Answer

Lowenstein-Jensen medium, because it contains inhibitors to stop other bacteria and selects for Mycobacterium tuberculosis.

Question 3

Which of the following is NOT a key part of aseptic technique in the laboratory?

Accepted Answer

Leaving culture plates open to the air for extended periods

Question 4

A sample is collected from a patient suspected of having typhoid fever. What is the most important labeling requirement for this sample?

Accepted Answer

Label as 'high risk' and include patient info, date, and type of sample

Question 5

Which of the following equations best represents the preparation of a chemically defined medium?

Accepted Answer

$$	ext{Chemically defined medium} = 	ext{Water} + 	ext{Exact amounts of carbon, nitrogen, energy, minerals}$$

Question 6

Why is it important to keep a flask at an angle when pouring agar plates?

Accepted Answer

To reduce contamination, control pouring, prevent bubbles, and make a smooth agar surface

Question 7

Which of the following best describes the difference between simple and complex media?

Accepted Answer

Simple media has a known composition, while complex media contains ingredients like blood or meat extract with unknown exact composition.

Question 8

A microbiologist is using EMB agar to isolate bacteria from a water sample. What result would indicate the presence of E. coli?

Accepted Answer

Colonies with a green sheen due to lactose fermentation

Question 9

Which of the following steps is NOT part of the proper aseptic handling of an inoculating loop?

Accepted Answer

Cool the loop by touching it to the bench before picking bacteria

Question 10

Which of the following best explains why some bacteria digest gelatin but not agar?

Accepted Answer

Gelatin is a protein that can be hydrolyzed by bacterial enzymes, while agar is a polysaccharide that most bacteria cannot digest.

Question 11

Which of the following is a correct application of Koch's postulates in proving a microbe causes a disease?

Accepted Answer

Isolate the suspected microbe from a diseased animal, grow it in pure culture, inoculate a healthy animal, and observe the same disease.

Question 12

Which of the following best describes the use of selective media?

Accepted Answer

Allows some bacteria to grow while inhibiting others, often using antibiotics, dyes, or salts

Question 13

A Gram stain is performed on a bacterial sample. The bacteria appear purple under the microscope. What does this indicate?

Accepted Answer

The bacteria are Gram-positive

Question 14

Which of the following is a reason why specimen transport media is used?

Accepted Answer

To preserve bacteria and prevent them from dying or overgrowing before analysis

Question 15

Which of the following best describes the composition of nutrient agar?

Accepted Answer

$$	ext{Nutrient agar} = 	ext{Peptones} + 	ext{Meat extract} + 	ext{Agar}$$

Question 16

Which of the following is a correct step in preparing culture media for bacterial growth?

Accepted Answer

Add agar to make solid media, autoclave, and cool before pouring into plates

Question 17

Why is it important to use aseptic technique when handling bacteria in the laboratory?

Accepted Answer

To prevent contamination of cultures and protect laboratory personnel

Question 18

Which of the following best describes the purpose of using blood agar in clinical microbiology?

Accepted Answer

To detect hemolysis patterns (alpha, beta, gamma) and support the growth of fastidious organisms

Question 19

A patient sample is delayed in transport to the laboratory. What is the recommended storage condition to preserve bacterial viability?

Accepted Answer

Store at $$4^\circ C$$

Question 20

Which of the following is a correct example of bacterial nomenclature according to the International Code of Nomenclature of Prokaryotes (ICNP)?

Accepted Answer

Escherichia coli (italicized)

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Study Guide - Practice Questions