Question 1

Which of the following best describes the principle of specificity in immunological testing?

Accepted Answer

An antibody binds only to a specific antigen, not to others.

Question 2

A laboratory is using the agglutination test to identify an unknown bacterial infection. After serial dilution of a patient's serum and addition of antigen, clumping is observed in tubes with higher concentrations of antibodies. What does this result indicate?

Accepted Answer

The patient has antibodies specific to the antigen, indicating exposure or infection.

Question 3

Which immunological method is most appropriate for detecting trace amounts of antigens or antibodies in a patient sample?

Accepted Answer

Enzyme-linked immunosorbent assay (ELISA)

Question 4

During a Western blot analysis for HIV, successive tests over 30 days show increasing band intensity. What does this observation most likely indicate?

Accepted Answer

Continued formation of anti-HIV antibodies in the patient

Question 5

In the polymerase chain reaction (PCR), what is the purpose of the denaturation step?

Accepted Answer

To separate the two strands of DNA by heating to $$94^	ext{\circ}C$$

Question 6

A patient’s serum is tested for five different antigens using a precipitation test in agar gel. Precipitated antigen-antibody complexes are observed for three antigens. What does this result suggest?

Accepted Answer

The patient has antibodies against three of the tested antigens.

Question 7

Which of the following is a genotypic method for identifying unknown microbes?

Accepted Answer

DNA analysis, such as PCR or genome sequencing

Question 8

In an indirect ELISA, which component from the patient sample is being detected?

Accepted Answer

Antibody

Question 9

A clinical laboratory is diagnosing Legionnaires’ disease using immunofluorescent testing. Which statement best describes the direct immunofluorescent method?

Accepted Answer

A fluorescent antibody is used to detect a specific antigen fixed on a slide.

Question 10

Which of the following equations best represents the exponential amplification of DNA during PCR after $$n$$ cycles, starting from a single DNA molecule?

Accepted Answer

$$N = 2^n$$

Question 11

A patient is suspected of having measles. Which ELISA method would be most appropriate for detecting measles virus antigens in the patient’s sample?

Accepted Answer

Capture (Sandwich) ELISA

Question 12

Which of the following is NOT a phenotypic method for identifying unknown microbes?

Accepted Answer

Genetic analysis using PCR

Question 13

In a precipitation test performed in agar gel, what is the expected result if a patient’s serum contains antibodies specific to the antigen placed in the center well?

Accepted Answer

A visible line of precipitate will form between the serum and antigen wells.

Question 14

Which of the following statements about the Western blot technique is correct?

Accepted Answer

It is highly specific and sensitive for detecting proteins.

Question 15

During PCR, which temperature range is used for the priming step, and what is its purpose?

Accepted Answer

$$50-65^	ext{\circ}C$$; to allow primers to base-pair with specific sites on the DNA

Question 16

Which of the following best explains why viruses are difficult to diagnose using traditional laboratory culture methods?

Accepted Answer

Viruses are not cells and require living host cells for replication.

Question 17

A patient’s serum is tested using a direct ELISA. What does a positive color change in the well indicate?

Accepted Answer

The presence of a specific antigen in the patient’s serum

Question 18

Which of the following is a key difference between agglutination and precipitation reactions in antigen-antibody testing?

Accepted Answer

Agglutination involves clumping of whole cells, while precipitation involves formation of complexes in cell-free solution.

Question 19

Which of the following laboratory techniques is most suitable for amplifying a specific DNA segment from a patient sample for genetic analysis?

Accepted Answer

Polymerase chain reaction (PCR)

Procedures for Identifying Pathogens and Diagnosing Infections: Laboratory and Molecular Methods in Microbiology

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