$$ DF = \frac{\text{Volume of sample}}{\text{Total volume}} $$

Question 1

Which of the following best describes the purpose of the Gram stain in microbiology?

Accepted Answer

To distinguish between bacteria with thick and thin peptidoglycan layers

Question 2

A sample is streaked onto MacConkey agar and produces pink colonies. What does this indicate about the bacteria?

Accepted Answer

The bacteria are Gram-negative and ferment lactose

Question 3

Which of the following media is used to differentiate bacteria based on their ability to ferment mannitol?

Accepted Answer

MSA

Question 4

A microbiologist observes clear zones around colonies on blood agar. What does this indicate?

Accepted Answer

Beta hemolysis

Question 5

Which of the following organisms is a protozoan that moves using cilia?

Accepted Answer

Paramecium caudatum

Question 6

Why is Sabouraud Dextrose Agar selective for fungi?

Accepted Answer

It has a low pH and high sugar content

Question 7

Which of the following is the correct interpretation of a positive starch hydrolysis test?

Accepted Answer

A clear zone appears around the colony after iodine is added

Question 8

A patient’s urine sample is streaked onto UTI Chromogenic agar and produces purple colonies. What does this result suggest?

Accepted Answer

Presence of Enterococcus species

Question 9

Which of the following is a distinguishing feature of Schistosoma mansoni eggs?

Accepted Answer

Presence of a lateral spine

Question 10

In the Kirby-Bauer disk diffusion test, which formula is used to calculate the diameter of the zone of inhibition?

Accepted Answer

$$ D = 2 	imes r $$

Question 11

Which of the following statements about Candida albicans is correct?

Accepted Answer

It is a yeast that can cause opportunistic infections

Question 12

Which of the following is the correct interpretation of a negative lactose fermentation result on MacConkey agar?

Accepted Answer

Colonies appear colorless

Question 13

Which of the following is a nematode that infects humans by penetrating the skin?

Accepted Answer

Necator americanus

Question 14

A microbiologist is testing for mannitol fermentation using MSA. Which result indicates a positive fermentation?

Accepted Answer

The medium turns yellow

Question 15

Which of the following is the correct formula for calculating the dilution factor in a serial dilution experiment?

Accepted Answer

$$ DF = \frac{	ext{Volume of sample}}{	ext{Total volume}} $$

Question 16

Which of the following is a distinguishing feature of Trypanosoma gambiense under the microscope?

Accepted Answer

Presence of flagella and undulating membrane

Question 17

Which of the following is the correct interpretation of a positive indole test?

Accepted Answer

A red ring forms at the top of the medium after adding Kovac’s reagent

Question 18

Which of the following is a common misconception about the use of differential media?

Accepted Answer

Differential media are only used to select for Gram-positive bacteria

Question 19

A blood agar plate shows greenish discoloration around colonies. What type of hemolysis is this?

Accepted Answer

Alpha hemolysis

Question 20

Which of the following is the correct sequence for using a microscope to observe bacteria?

Accepted Answer

Begin with low power, focus, then move to high power and oil immersion

Microbiology Lab Final Study Guide: Microbial Identification, Media, and Tests

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