Question 1

Which of the following best explains why 16S rRNA gene sequencing is considered the 'gold standard' for bacterial identification?

Accepted Answer

It is found in all domains of life, is functionally constant, sufficiently conserved, and of sufficient length.

Question 2

A clinical isolate is a Gram-positive, catalase-negative, non-motile rod that produces acid only from glucose fermentation. Which genus does it most likely belong to?

Accepted Answer

Lactobacillus

Question 3

Which of the following is a distinguishing feature of the cell wall in Mycobacterium species?

Accepted Answer

High content of mycolic acids

Question 4

A patient presents with gas gangrene after a traumatic injury. Which organism is most likely responsible, and what is a key identifying feature?

Accepted Answer

Clostridium perfringens; anaerobic, endospore-forming rod

Question 5

Which phylum contains the largest number of characterized bacterial genera and includes many important pathogens such as Escherichia coli?

Accepted Answer

Proteobacteria

Question 6

Which of the following best describes the concept of a 'core genome' as shown in the pangenome Venn diagram?

Accepted Answer

Genes shared by all compared organisms

Question 7

Which laboratory method would be most appropriate for distinguishing between Streptococcus and Staphylococcus species?

Accepted Answer

Catalase test

Question 8

A Gram-negative, facultative rod ferments lactose to acid and gas and is positive for indole and methyl red tests but negative for citrate and Voges-Proskauer. What is the most likely identification?

Accepted Answer

Escherichia coli

Question 9

Which of the following statements about Archaea is correct?

Accepted Answer

They often inhabit extreme environments and have unique membrane lipids.

Question 10

Which of the following is a key difference between Firmicutes and Actinobacteria?

Accepted Answer

Firmicutes have low G+C content, Actinobacteria have high G+C content.

Question 11

Which of the following best describes the role of Average Nucleotide Identity (ANI) in microbial taxonomy?

Accepted Answer

It compares nucleotide sequences in conserved regions to define species boundaries, with a cutoff of 95%.

Question 12

Which genus is known for producing antibiotics such as streptomycin and tetracycline, and exhibits a filamentous, fungal-like morphology?

Accepted Answer

Streptomyces

Question 13

A patient is diagnosed with tuberculosis. Which feature of the causative agent contributes to its resistance to desiccation and many antibiotics?

Accepted Answer

Presence of a waxy, mycolic acid-rich cell wall

Question 14

Which of the following is a characteristic of Enterobacteriaceae family members?

Accepted Answer

Facultative anaerobic rods that ferment glucose

Question 15

Which of the following best describes the function of immunodiagnostic (serology) tests in microbial identification?

Accepted Answer

Detection of antigen-antibody reactions

Question 16

Which of the following is a unique feature of Spirochaetes?

Accepted Answer

Motility via axial filaments resulting in corkscrew movement

Question 17

Which of the following is a medically significant member of the genus Neisseria, and what disease does it cause?

Accepted Answer

N. meningitidis; meningococcal meningitis

Question 18

Which of the following best describes the main difference between the cell wall structures of Bacteria and Archaea?

Accepted Answer

Bacteria have peptidoglycan, Archaea have pseudomurein.

Question 19

Which of the following is a correct application of a dichotomous key in bacterial identification?

Accepted Answer

Using a series of yes/no questions based on observable traits to narrow down the identity of an unknown bacterium.

Microbial Systematics and Prokaryotic Diversity: Study Notes

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