Question 1

Which of the following best describes the difference between bacteriophage lytic and lysogenic cycles?

Accepted Answer

The lytic cycle results in immediate destruction of the host cell, while the lysogenic cycle involves integration of phage DNA into the host genome without immediate lysis.

Question 2

A microbiologist is calculating the titer of a T4 virus stock. If 0.1 mL of a 10	extsuperscript{-6} dilution produces 50 plaques, what is the titer in PFU/mL? Use the formula $$	ext{Titer} = \frac{	ext{Number of plaques}}{	ext{Dilution} 	imes 	ext{Volume plated (mL)}}.$$

Accepted Answer

$$5 	imes 10^8$ PFU/mL

Question 3

Which of the following best explains why MacConkey agar is used to differentiate bacteria in a mixed culture?

Accepted Answer

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

Question 4

Which of the following is a distinguishing feature of mold versus yeast when viewed microscopically?

Accepted Answer

Molds form hyphae and spores, while yeasts reproduce by budding and are unicellular.

Question 5

A student observes a bacterial colony with a green metallic sheen on EMB agar. What does this indicate about the organism?

Accepted Answer

It is a Gram-negative bacterium that rapidly ferments lactose, such as Escherichia coli.

Question 6

Which test would best differentiate between Staphylococcus aureus and Staphylococcus epidermidis?

Accepted Answer

Coagulase test

Question 7

A throat swab is streaked on blood agar and produces clear, complete hemolysis around the colonies. Which type of Streptococcus is most likely present?

Accepted Answer

Beta Streptococcus

Question 8

Which of the following best describes the appearance of alpha hemolysis on blood agar?

Accepted Answer

Greenish or partial discoloration around colonies

Question 9

A Gram-negative rod is isolated and produces a red color after addition of methyl red reagent. What does this indicate about the organism's metabolism?

Accepted Answer

It performs mixed acid fermentation.

Question 10

Which of the following is a key difference between Enterobacteriaceae and non-Enterobacteriaceae Gram-negative rods?

Accepted Answer

Enterobacteriaceae ferment glucose, while non-Enterobacteriaceae often do not.

Question 11

A patient sample is streaked on CNA agar and only Gram-positive cocci grow. What is the purpose of CNA agar in this scenario?

Accepted Answer

To inhibit Gram-negative bacteria and select for Gram-positive cocci

Question 12

Which of the following best explains why it is important to spell Alpha Streptococcus and Beta Streptococcus correctly and use correct binomial nomenclature in lab reports?

Accepted Answer

Incorrect spelling can lead to confusion with unrelated organisms and misinterpretation of results.

Question 13

A microbiologist is asked to identify an unknown Gram-negative rod using the IMViC tests. Which combination of results would most likely indicate Escherichia coli?

Accepted Answer

Indole positive, Methyl Red positive, Voges-Proskauer negative, Citrate negative

Question 14

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

Accepted Answer

To isolate individual colonies from a mixed culture

Question 15

A student is asked to distinguish between Staphylococcus and Streptococcus using a simple biochemical test. Which test should they use?

Accepted Answer

Catalase test

Question 16

Which of the following is a common misconception about the use of blood agar in clinical microbiology?

Accepted Answer

Blood agar is a selective medium that only allows Gram-positive bacteria to grow.

Question 17

A microbiologist observes a bacterial colony that is catalase positive and coagulase negative. Which organism is most likely present?

Accepted Answer

Staphylococcus epidermidis

Question 18

Which of the following best explains why Enterococcus faecalis can be differentiated from other alpha hemolytic streptococci?

Accepted Answer

It can grow in 6.5\% NaCl and hydrolyze esculin.

Question 19

A patient sample is tested using the KIA (Kligler Iron Agar) test and produces a yellow butt and red slant. What does this result indicate?

Accepted Answer

Glucose fermentation only

Question 20

Which of the following is the best approach to identifying an unknown bacterium from a mixed culture using a dichotomous key?

Accepted Answer

Perform a series of biochemical tests and follow the branching logic of the key based on results.

Final Lab Practical Study Guide: Microbiology Lab Techniques and Identification

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