Question 1

Which of the following is an example of a correctly written and spelled species name for a normal skin microbiota?

Accepted Answer

Staphylococcus epidermidis

Question 2

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media allows only certain bacteria to grow, while differential media distinguishes between bacteria based on observable changes.

Question 3

A black colony surrounded by a zone of white precipitation on Baird-Parker Agar is most likely caused by which of the following reactions?

Accepted Answer

Tellurite reduction and lecithinase activity

Question 4

Which compound in Mannitol Salt Agar makes it selective for Staphylococcus species?

Accepted Answer

Sodium chloride (NaCl)

Question 5

The catalase test is used to differentiate between which groups of bacteria?

Accepted Answer

Staphylococci (catalase positive) and Streptococci (catalase negative)

Question 6

Which of the following best describes the reaction catalyzed by catalase?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 7

In an epidemic simulation lab, the pattern of a common source epidemic would most likely be represented by which type of graph?

Accepted Answer

A sharp rise in cases followed by a rapid decline

Question 8

Which of the following statements about LPS (lipopolysaccharide) is TRUE?

Accepted Answer

LPS is an endotoxin found in the outer membrane of Gram-negative bacteria and is heat-stable.

Question 9

Which two pathogens are most commonly associated with foodborne illness from chicken?

Accepted Answer

Campylobacter jejuni and Salmonella enterica

Question 10

Which medium would you use to detect coliforms in a food sample, and what is the key differential reaction?

Accepted Answer

VRB-MUG Agar; blue fluorescence under UV light due to $$\beta-$$glucuronidase activity

Question 11

A food sample is diluted as follows: 25 g of food is blended with 225 mL of diluent. What is the dilution factor of the initial mixture?

Accepted Answer

$$\frac{1}{10}$$

Question 12

Which of the following best describes the microscopic appearance and oxygen requirements of Campylobacter jejuni?

Accepted Answer

Gram-negative curved rods, microaerophilic

Question 13

Why is a stomacher machine used in food microbiology sample preparation?

Accepted Answer

To homogenize the food sample, ensuring even distribution of microbes

Question 14

Which of the following is the correct definition of a fecal coliform?

Accepted Answer

A coliform that can ferment lactose with gas production at 44.5°C

Question 15

You observe a petri plate with three distinctly different colony morphologies. Which of the following is the best interpretation?

Accepted Answer

There are three different species or types of microorganisms present.

Question 16

Which of the following best describes the purpose of streaking for isolation?

Accepted Answer

To obtain single, isolated colonies from a mixed culture

Question 17

A student performs a Gram stain and observes pink, curved rods under the microscope. Which organism is this most consistent with?

Accepted Answer

Campylobacter jejuni

Question 18

Which of the following is NOT a correct observation to record when describing a bacterial colony?

Accepted Answer

Gram reaction

Question 19

Which of the following techniques is essential for preventing contamination when inoculating media?

Accepted Answer

Aseptic technique

Question 20

A sample is serially diluted 1:10 three times. What is the final dilution factor?

Accepted Answer

$$\frac{1}{1000}$$

Microbio lab exam #1

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