Q: Which equation best represents the calculation of average nucleotide identity (ANI) between two bacterial genomes?

$$\text{ANI} = \frac{\text{Number of identical nucleotides}}{\text{Total number of nucleotides compared}} \times 100$$

Question 1

Which of the following methods is most appropriate for rapidly identifying a bacterial species that cannot be cultured in the laboratory?

Accepted Answer

Sequencing 16S rRNA genes

Question 2

A clinical laboratory uses a dichotomous key to identify a Gram-positive coccus. The organism is catalase-positive and coagulase-positive. Which species is most likely present?

Accepted Answer

Staphylococcus aureus

Question 3

Which of the following statements about the three-domain system is correct?

Accepted Answer

It divides prokaryotes into Bacteria and Archaea based on ribosomal RNA sequences.

Question 4

A laboratory technician observes red colonies at 22°C and a fruity odor from a culture. Which organism is most likely present?

Accepted Answer

Serratia marcescens

Question 5

Which equation best represents the calculation of average nucleotide identity (ANI) between two bacterial genomes?

Accepted Answer

$$	ext{ANI} = \frac{	ext{Number of identical nucleotides}}{	ext{Total number of nucleotides compared}} 	imes 100$$

Question 6

Which identification method relies on the detection of specific antigens on the surface of bacterial cells?

Accepted Answer

Serological testing

Question 7

A sample is analyzed by MALDI-TOF mass spectrometry. What is the primary result used for identification?

Accepted Answer

A mass spectrum fingerprint of proteins

Question 8

Which of the following is a limitation of nucleic acid probes in microbial identification?

Accepted Answer

They can only detect a single possibility per probe.

Question 9

Which method is most useful for distinguishing between closely related strains of Escherichia coli in a foodborne outbreak investigation?

Accepted Answer

Whole genome sequencing (WGS)

Question 10

If two bacterial strains have a DNA-DNA hybridization similarity of 80%, what does this indicate?

Accepted Answer

They are considered members of the same species.

Question 11

Which of the following best explains why ribosomal RNA genes are reliable for phylogenetic analysis?

Accepted Answer

They perform essential functions and tolerate only limited mutations.

Question 12

A patient sample is tested for urease activity using a breath test. Which organism is most likely being identified?

Accepted Answer

Helicobacter pylori

Question 13

Which of the following statements about G+C content is correct?

Accepted Answer

DNA with higher G+C content melts at a higher temperature due to more hydrogen bonds.

Question 14

Which of the following is a real-world application of phage typing?

Accepted Answer

Tracing the source of a bacterial outbreak in a hospital

Question 15

Which of the following is a reason why phenotypic methods are still important in microbial identification?

Accepted Answer

They provide a foundation for identification and can be used when molecular methods are unavailable.

Question 16

Which of the following best describes the hierarchical order of taxonomic classification from most specific to most general?

Accepted Answer

Species, Genus, Family, Order, Class, Phylum, Kingdom, Domain

Question 17

Which of the following is a limitation of using 16S rRNA gene sequencing for species-level identification?

Accepted Answer

Closely related prokaryotes can have identical 16S rRNA sequences.

Question 18

Which of the following is a function of Bergey’s Manual of Systematic Bacteriology?

Accepted Answer

It describes all known prokaryotic species and classifies them according to genetic relatedness.

Question 19

Which of the following is a real-world use of WGS data networks such as PulseNet?

Accepted Answer

Tracking foodborne outbreaks nationally and globally

Question 20

Which of the following best describes the principle behind DNA-DNA hybridization?

Accepted Answer

The extent of hybridization reflects the degree of sequence similarity between two organisms.

Microbial Taxonomy: Identification and Classification of Microorganisms

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