Question 1

The indirect ELISA test is commonly used to diagnose infections caused by all of the following except

Accepted Answer

Rubella virus is not diagnosed using the indirect ELISA test.

Question 2

Your daughter probably has strep throat,caused by Streptococcus pyogenes.The traditional method of diagnosis involves culturing on blood agar,but this process is time consuming.Your doctor wants a more rapid identification of the infectious agent using a specimen directly obtained from the patient's throat using a test that can be read in his office,without having to culture and isolate the organism.He would likely choose the:

Accepted Answer

The immunochromatographic test is a rapid diagnostic test that can detect the presence of Streptococcus pyogenes directly from a throat swab specimen. It utilizes antibodies to detect the group A carbohydrate antigen in the bacteria. This test can be conducted in the doctor's office and provides results within minutes, thereby allowing for prompt treatment of the patient. The other options mentioned in the question (direct fluorescence test, Western Blot test, pulse-field gel electrophoresis) are not typically used for the rapid diagnosis of strep throat in a clinical setting.

Question 3

When minute samples of DNA need to be genetically analyzed for identification purposes,which test can be effectively used?

Accepted Answer

PCR (polymerase chain reaction) is a method used to amplify small amounts of DNA into millions of copies. This makes it an effective choice for genetic identification purposes when only minute samples of DNA are available. Direct fluorescence antibody, Widal, Weil-Felix reaction, and Western Blot are not used for genetic identification purposes.

Question 4

The tuberculin skin test is read

Accepted Answer

The tuberculin skin test (TST), also known as the Mantoux test, is read from 48 to 72 hours after administration. This time frame allows for an adequate immune response to develop at the site of injection, which is then measured to determine the presence of a latent or active tuberculosis infection.

Question 5

Both pulse-field gel electrophoresis and Western blotting utilize electrophoresis in their procedures.When comparing the two procedures,which statement is true?

Accepted Answer

Pulse-field gel electrophoresis is used for genetic analysis and separates DNA fragments, while Western blotting separates proteins and can identify antibodies in a specimen. Pulse-field gel electrophoresis is also excellent for identifying genetic differences among strains.

Question 6

Mycobacterium tuberculosis has traditionally been identified in patient samples using biochemical tests,and more recently through DNA probe analysis.In vivo testing can also be completed using the tuberculin skin test.
A more recent test that seems to be surpassing the others is the QuantiFERON-TB gold test.Blood samples are mixed with protein antigens of M.tuberculosis.After 16 to 24 hours of incubation,the amount of the cytokine interferon produced by the patientt's cells is measured.If the patient is infected with M.tuberculosis,their WBCs will release interferon in response to contact with the tuberculosis protein antigens.This test falls under which category of identification tests?

Accepted Answer

The QuantiFERON-TB gold test is an immunologic test, as it measures the immune system's response to M. tuberculosis antigens by detecting the production of interferon by the patient's WBCs.

Question 7

The direct ELISA test is used to diagnose all of the following except

Accepted Answer

The direct ELISA test can be used to detect the presence of specific antigens or antibodies in a patient's sample. In the case of the options provided, it can be used to diagnose hantavirus (A), rubella virus (B), and Toxoplasma (D). However, it cannot be used to diagnose past exposure to Mycobacterium tuberculosis (C), as this requires a different type of test such as a tuberculin skin test or interferon-gamma release assay.

Question 8

The ELISA test has been used as the most common,rapid screening test for HIV infection.Its sensitivity is very high but its specificity is rather low (for an important identification test).Which statement describes this accurately?

Accepted Answer

The ELISA test has a high rate of false positives because it may capture normal antibodies present in the patient's blood, leading to a positive result even if the patient is not infected with HIV. The test has high sensitivity because it can detect very small amounts of HIV antibodies, but its low specificity can lead to false positives. The other answer choices are not accurate descriptions of the ELISA test.

Question 9

The patient's vaginal specimen is sent from the walk-in clinic to the microbiology laboratory.There it is cultured on bacteriological media,and then placed into an ambient air incubator set at 22% oxygen and 37 degrees Celsius.The patient is strongly suspected of having gonorrhea.She had sexual contact with a partner recently diagnosed with gonorrhea,and is now displaying the typical symptoms of a vaginal exudate or fluid.Neisseria gonorrhoeae is a microaerophilic gram-negative coccus-shaped bacterium.Seventy-two hours later,the culture has still not grown Neisseria gonorrhoeae so the lab reports the results back as negative.Interpret this result.

Accepted Answer

Neisseria gonorrhoeae is a microaerophilic bacterium, which requires a specific environment with less oxygen (22%) than the normal air for growth. Therefore, it is possible that the sample was cultured in an inappropriate environment, leading to the negative result. Other factors mentioned in the answer choices are less likely to be the cause of the negative result.

Question 10

When antibodies or other substances in serum cross-react with the test reagents,a false positive result can occur.

Accepted Answer

Cross-reactivity occurs when an antibody in the serum recognizes and binds to a reagent used in the test, leading to a false positive result.

Question 11

The tuberculin test is an example of an in vitro serological test.

Accepted Answer

The tuberculin test is an example of an in vivo test, where a substance is injected into the skin to test for a reaction. Serological tests are in vitro tests that measure the presence of antibodies or antigens in a person's blood or other bodily fluids. Examples of serological tests include ELISA, Western blot, and rapid diagnostic tests for HIV.

Question 12

Serological testing always involves reactions between specific antibody and antigen.

Accepted Answer

Serological testing is a type of laboratory diagnostic testing that involves the use of specific antibodies and antigens to detect the presence of a particular disease or infection in a patient's blood or other bodily fluids. The test works by detecting the specific interaction between the patient's antibodies and the antigens used in the test, which can help identify the presence or absence of a particular disease or infection.

Question 13

Dr.John Doe,a research microbiologist for a university medical center,has been accused of sending Bacillus anthracis,the causative agent of anthrax,through the mail to the President.You,as a public health official with the CDC,have to determine if it is the same strain as the two strains of B. anthracis found cultured in his lab.Which method of identification would you use to compare these three bacterial samples?

Accepted Answer

Pulse-field gel electrophoresis (PFGE) is a technique that separates large DNA molecules based on their sizes using an electric field. PFGE is a highly discriminative technique that can identify small genetic differences among strains of the same bacterial species, and is ideal for comparing strains suspected to be closely related. Therefore, PFGE is the best choice for identifying if the strain of B. anthracis sent in the mail is the same as those cultured in Dr. Doe's lab.

Question 14

The polymerase chain reaction requires endonuclease to cut samples of DNA.

Accepted Answer

The polymerase chain reaction (PCR) does not require endonuclease (restriction enzymes) to cut samples of DNA. PCR amplifies specific regions of DNA using primers and a DNA polymerase enzyme.

Question 15

ELISA tests use a fluorescent dye as a label to trace antigen-antibody reactions.

Accepted Answer

ELISA (enzyme-linked immunosorbent assay) tests use an enzyme as a label, not a fluorescent dye. The enzyme catalyzes a reaction that produces a detectable signal.

Question 16

A positive direct ELISA result requires

Accepted Answer

The answer of A positive direct ELISA result requires
...

Question 17

The urine specimen obtained from a patient went to the microbiology lab for a bacterial culture and antibiotic sensitivity testing.The specimen sat out on the processing counter for a couple of hours before being cultured.Twenty fours hours later,the lab report goes into the computer---over 100,000 bacterial cells per milliliter of urine.Which statement is an accurate assessment of these results?

Accepted Answer

Leaving the urine specimen out on the processing counter for a couple of hours before culturing it could lead to the growth of contaminants, which could overgrow actual bacteria in the sample. Refrigeration could have stalled the growth of contaminants and bacteria alike, hence increasing the accuracy of the bacterial count.

Question 18

It is necessary to do lab tests to diagnose all diseases.

Accepted Answer

Not all diseases require lab tests for diagnosis. Some may be diagnosed based on symptoms and physical examination alone. However, lab tests can be helpful in confirming a diagnosis or ruling out certain conditions.

Question 19

The ELISA is commonly used for diagnosing salmonellosis.

Accepted Answer

ELISA (Enzyme-Linked Immunosorbent Assay) is commonly used for detecting and quantifying substances such as peptides, proteins, antibodies, and hormones. For diagnosing salmonellosis, culture methods or PCR (Polymerase Chain Reaction) are more commonly used to directly detect Salmonella bacteria.

Question 20

Serological tests should have low sensitivity and specificity.

Accepted Answer

Serological tests should have high sensitivity and specificity to accurately detect the presence or absence of antibodies in a sample. Low sensitivity or specificity can lead to false negative or false positive results, respectively.

Quiz 17: Diagnosing Infections