Question 1

A 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

The accuracy of bacterial counts in urine cultures can be compromised if the sample is not processed or refrigerated promptly. Bacteria can multiply rapidly at room temperature, leading to an overestimation of the bacterial load present in the original sample.

Question 2

Microarrays, hybridization tests, and ribotyping are increasing in frequency in their use in clinical labs for diagnosis of infectious diseases and the microorganisms causing them. Why is this?

Accepted Answer

Genomic testing, including methods like microarrays, hybridization tests, and ribotyping, tends to have fewer errors compared to traditional biochemical and serological tests. This is because these methods directly analyze the genetic material of microorganisms, allowing for more precise identification.

Question 3

If you were going to identify microorganisms within a specimen containing large numbers of organisms (seawater, normal microbiota, etc.), you would have to ______.

Accepted Answer

Amplifying gene sequences within the sample is a common method for identifying different organisms in a complex mixture, such as seawater or normal microbiota. This approach, often involving PCR (Polymerase Chain Reaction), allows for the specific identification of microorganisms based on their genetic material.

Question 4

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

Accepted Answer

The tuberculin test is actually an in vivo test that involves injecting a small amount of tuberculin into the skin and observing the resulting reaction. It is not a serological test, which typically involves detecting antibodies or antigens in blood or other bodily fluids.

Question 5

Which test cannot be used for identiﬁcation of a person's HIV status?

Accepted Answer

Biochemical tests are not used for identifying a person's HIV status. They are generally used to assess the overall health and function of organs and systems in the body. HIV status is determined through specific tests that detect the presence of HIV antibodies or antigens, such as Immunochromatographic testing, Western Blot, and ELISA.

Question 6

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

Accepted Answer

The polymerase chain reaction (PCR) does not require endonuclease to cut samples of DNA. PCR is a technique used to amplify a specific segment of DNA, and it involves repeated cycles of denaturation, annealing, and extension. Enzymes used in PCR include Taq polymerase, which adds nucleotides to the DNA strand, and primers, which provide a starting point for the polymerase to add nucleotides. Endonucleases are not necessary for PCR.

Question 7

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

Accepted Answer

All the statements are true. Pulse-field gel electrophoresis (PFGE) is indeed used for genetic analysis, specifically to separate large DNA fragments by applying an electric field that periodically changes direction. This technique is excellent for identifying genetic differences among strains of a single species, making it valuable in epidemiological studies. Western blotting, on the other hand, is a method used to separate proteins and can be used to identify the presence of specific antibodies in a patient's specimen, making it useful in the diagnosis of various diseases.

Question 8

Which statement about clinical identiﬁcation tests is true?

Accepted Answer

Not all diseases can be identified by clinical tests, as some may require clinical evaluation, imaging, or other diagnostic methods beyond laboratory tests.

Question 9

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

Accepted Answer

ELISA tests use an enzyme or a colorimetric reaction as a label, not a fluorescent dye.

Question 10

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

Accepted Answer

The low specificity of the ELISA test means it may sometimes react with non-HIV antibodies present in the blood, leading to false positive results. This is because the test antigens used in ELISA can sometimes bind to normal antibodies that are not specific to HIV.

Question 11

Which of these tests is an in vivo test?

Accepted Answer

The Tuberculin test is an in vivo test because it involves injecting tuberculin PPD into the skin and observing the body's immune response to it, which takes place within the living organism.

Question 12

A 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 she is now displaying the typical symptoms of a vaginal exudate or ?uid. 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, being a microaerophilic organism, requires environments with lower oxygen levels than what is present in ambient air (22% oxygen). The standard incubation environment for cultivating Neisseria gonorrhoeae typically involves increased CO2 (around 3-5%) and lower O2 levels than those found in ambient air, which likely explains the failure of the culture to grow.

Question 13

You place an inoculum of your bacterium on a glass slide and add a drop of hydrogen peroxide reagent. Promptly you see bubbles appear, indicating the presence of a particular enzyme that the bacterium produces. What type of identi?cation test does this exemplify?

Accepted Answer

This is a biochemical test because it involves adding a chemical reagent (hydrogen peroxide) to the bacterium to observe a biochemical reaction (bubbling due to the production of oxygen gas), which indicates the presence of the enzyme catalase.

Question 14

Nucleic acid testing is appropriate as a testing method when one is not sure what microorganisms are present in the specimen.

Accepted Answer

Nucleic acid testing can detect the presence of specific genetic material of microorganisms in a sample, making it useful when identifying unknown pathogens present in a specimen.

Question 15

Mycobacterium tuberculosis has traditionally been identi?ed 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 patient'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 identi?cation tests?

Accepted Answer

The QuantiFERON-TB gold test is an immunologic test because it measures the immune response (specifically, the production of interferon gamma) to M. tuberculosis antigens.

Question 16

The polymerase chain reaction can be used for identiﬁcation of ______.

Accepted Answer

The polymerase chain reaction (PCR) is a technique used to amplify small segments of DNA. It is commonly used for the identification of microorganisms by amplifying and analyzing their unique genetic sequences.

Question 17

Staphylococcus aureus can be identiﬁed by mixing the organism with speciﬁc antibody and visually recognizing a clumping reaction between the antigen and the antibody. This is a/an _______ test.

Accepted Answer

Agglutination tests involve the clumping of particles (such as bacteria) in the presence of an antibody that specifically binds to an antigen on the surface of those particles, which is the mechanism described for identifying Staphylococcus aureus.

Question 18

You would like to identify as many bacterial species as possible in the human mouth. Why is biochemical testing not the most eﬃcient and accurate method of completing this task?

Accepted Answer

Biochemical testing relies on knowing the growth characteristics and metabolic properties of bacteria to select appropriate media for isolation and culture. Without this knowledge, it's challenging to identify all bacterial species in a diverse environment like the human mouth.

Question 19

You are the supervisor of a new reference microbiology laboratory, which will receive clinical specimens for identi?cation of bacterial pathogens. When choosing the types of media to order for culture and isolation procedures in your laboratory, what question(s) do you need to answer?

Accepted Answer

All of the choices are correct because understanding the type of bacteria you will be culturing, the growth factors required by those bacteria, and the kind of microbiota present in patient specimens are all crucial for selecting the appropriate media for culture and isolation procedures in a microbiology laboratory.

Question 20

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 identi?cation of the infectious agent using a specimen directly obtained from the patient's throat. He would prefer to use a test that can be read in his o?ce 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 be used directly on patient samples, such as a throat swab, to detect the presence of Streptococcus pyogenes antigens. This makes it suitable for use in a doctor's office for quick diagnosis of strep throat without the need for culturing.

Quiz 17: Diagnosing Infections