Deck 20: Serological and Molecular Detection of Bacterial Infections

Question 1

Which of the following statements best describes how lateral flow assays demonstrate the presence of bacterial,fungal,and viral antigens?

A) During the assay, bacterial antigens present in a specimen are pretreated by coating them with colloidal gold prior to binding to an antibody.
B) A positive test results from the binding of the conjugated antibody and antigen to a fixed antibody directed against the antigen in the capture zone.
C) A positive test results from the precipitation of the antigen-antibody complex in the capture zone.
D) Migration of labeled antigen to the capture zone produces a positive result.

Answer 1

A positive test results from the binding of the conjugated antibody and antigen to a fixed antibody directed against the antigen in the capture zone.

Question 2

Which of the following is an advantage of bacterial culture in diagnosing an infection?

A) Standardized, selective media can differentiate bacteria based on their ability to grow.
B) All bacteria can be easily evaluated by culture.
C) The method is very rapid.
D) The method rarely poses risks to laboratory personnel.

Answer 2

Standardized, selective media can differentiate bacteria based on their ability to grow.

Question 3

Which test is inappropriate for identifying Helicobacter pylori?

A) Polymerase chain reaction
B) Urease
C) Enzyme immunoassay
D) DNase

Answer 3

DNase

Question 4

The M protein of group A streptococci inhibits:

A) antibody binding.
B) phagocytosis.
C) T-cell apoptosis.
D) lymphocyte proliferation.

Question 5

Which statement regarding exotoxins and endotoxins is true?

A) Endotoxins and exotoxins are highly immunogenic, allowing for the development of protective antibodies and vaccines.
B) Endotoxin has targeted activity, whereas exotoxins have systemic effects when released.
C) Endotoxin is released from the cell wall of dead bacteria, whereas exotoxin is released from live bacteria.
D) Endotoxins and exotoxins bind to specific receptors on a bacterial cell, leading to the pathological events associated with the toxins.

Question 6

Select the true statement about Helicobacter pylori.

A) It is a gram-positive coccus that causes skin infections.
B) It is a gram-negative spiral bacterium that causes ulcers.
C) It lacks a cell wall and produces a lot of acid.
D) It can be detected by testing for cold agglutinins.

Question 7

Antibodies against streptolysin O,hyaluronidase,and DNase B are measured in the diagnosis of which disease?

A) Streptococcal pharyngitis
B) Acute rheumatic fever
C) Rheumatoid arthritis
D) Systemic lupus erythematosus

Question 8

The pathogenesis of poststreptococcal glomerulonephritis involves:

A) deposition of immune complexes in the kidneys.
B) destruction of glomeruli by streptolysin O.
C) bacterial-induced dehydration.
D) invasion of the kidneys by Streptococcus pyogenes.

Question 9

An anti-streptolysin O enzyme inhibition test was performed on the serum of a 10-year-old female patient with the following results: no hemolysis in the 1:10,1:20,1:40,and 1:80 tubes; hemolysis in the 1:160,1:320,and 1:640 tubes.What conclusion can you draw from these results?

A) The titer is 1:640, and the patient may have glomerulonephritis.
B) The titer is 1:160, and the patient may have rheumatic fever.
C) The titer is 1:80, and the patient is normal.
D) The test is invalid and must be repeated.

Question 10

The genetic determinants for the structural features of bacteria are encoded in:

A) single-stranded DNA.
B) plasmids.
C) double-stranded RNA.
D) chromosomal DNA.

Question 11

Complement helps in the defense against bacterial invasion by:

A) promoting phagocytosis.
B) neutralizing bacterial toxins.
C) preventing bacteria from penetrating the skin.
D) fusing lysosomal granules to bacterial cell walls.

Question 12

A symbiotic relationship in which both the microorganism and the host benefit is called:

A) commensal.
B) mutualistic.
C) parasitic.
D) virulent.

Question 13

The pathogenesis of Rocky Mountain spotted fever involves:

A) systemic release of cytokines, leading to toxic shock.
B) endothelial cell damage, leading to increased vascular permeability.
C) release of potent exotoxins that destroy vascular endothelium.
D) invasion of the organism into the cardiac muscle.

Question 14

The advantage of microscopic visualization in bacterial diagnosis is that the method is:

A) very sensitive.
B) easy to perform.
C) easy to interpret.
D) able to identify all clinically relevant microbes.

Question 15

What is the main reason testing for cold agglutinins is no longer recommended to diagnose infection with Mycoplasma pneumonia?

A) It is difficult to perform.
B) False positives may be caused by certain viruses.
C) Very few people develop anti-I antibodies.
D) It requires expensive instrumentation.

Question 16

Which of the following bacterial enzymes causes the release of lysosomal contents into the cytoplasm of the phagocytic cell,leading to the death of the cell?

A) Protein H
B) Leukocidin
C) M protein
D) IgA protease

Question 17

Genetic coding for virulence factors can be transferred among various bacteria by:

A) single-stranded DNA.
B) plasmids.
C) double-stranded RNA.
D) chromosomal DNA.

Question 18

Antibodies detected by reacting patient serum with rickettsial antigens,followed by incubation with an anti-immunoglobulin with a fluorescent tag,could be used to diagnose:

A) Rocky Mountain spotted fever.
B) Mycoplasma pneumonia.
C) stomach ulcers.
D) rheumatic fever.

Question 19

Identify the true statement about exotoxins.

A) They are structural proteins on the exterior surface of bacteria.
B) They nonspecifically activate host complement and coagulation cascades.
C) They bind to specific receptors on host cells.
D) They promote bacterial adhesion.

Question 20

Obligate intracellular,gram-negative bacteria best describes:

A) Streptococcus pyogenes.
B) Helicobacter pylori.
C) Rickettsia prowazekii.
D) Mycoplasma pneumonia.

Question 21

The cold agglutinins that develop in patients infected with Mycoplasma pneumoniae are:

A) IgG specific for M pneumoniae.
B) IgG specific for M pneumoniae exotoxin.
C) IgM that reacts with I antigen on red blood cells.
D) IgM that reacts with ASO antigens on M pneumoniae.

Question 22

The ability of an organism to cause disease is known as its:

A) virulence.
B) infectivity.
C) resistance.
D) pathogenicity.

Question 23

The advantage of molecular assays in bacterial diagnosis is:

A) many methods approved by the Food and Drug Administration are available.
B) the instrumentation is not expensive.
C) the reagents and disposables are not expensive.
D) the methods are very sensitive.

Question 24

Which bacterium is transmitted via the fecal-oral route?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori

Question 25

A noninvasive breath test can be used to diagnose:

A) Streptococcus pyogenes.
B) Mycoplasma pneumoniae.
C) Rickettsia rickettsii.
D) Helicobacter pylori.

Question 26

Which bacterial infections are routinely diagnosed by measuring host antibodies that neutralize the microbe's exotoxins?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori

Question 27

Which bacterium is transmitted to humans via tick or flea bites?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori

Question 28

Which of the following is the first reaction in a lateral flow immunochromatographic assay?

A) Antigen reacts with a labeled antibody.
B) Antigen is captured by antibody immobilized at a specific location on a membrane.
C) Labeled antibody is captured by membrane-immobilized antibody.
D) Antibody reacts with a labeled antigen.

Question 29

Stevens-Johnson syndrome,in which the top layer of the skin dies and sheds,is caused by:

A) Streptococcus pyogenes.
B) Mycoplasma pneumoniae.
C) Rickettsia rickettsii.
D) Helicobacter pylori.

Question 30

The gold standard for diagnosing Rickettsia rickettsii infection is:

A) culture.
B) molecular methods.
C) microscopy.
D) indirect immunofluorescence.

Question 31

Helicobacter pylori secretes urease to:

A) protect itself from a harsh environment.
B) breach the mucosal barriers of the host.
C) inactivate neutrophils.
D) increase its virulence.

Question 32

A primary disadvantage of using serology in the diagnosis of an infection is:

A) cost.
B) delayed appearance of antibodies after onset of infection.
C) sensitivity.
D) biologic hazard to laboratory personnel.

Question 33

Acute glomerulonephritis can be a sequela of infection by:

A) Streptococcus pyogenes.
B) Mycoplasma pneumoniae.
C) Rickettsia rickettsii.
D) Helicobacter pylori.

Question 34

Which of the following is an endotoxin,not an exotoxin?

A) Streptolysin O
B) Lipid A
C) Streptokinase
D) Hyaluronidase

Question 35

In general,antigen detection assays in bacterial diagnosis have which of the following characteristics?

A) High associated cost
B) Rapid turnaround time
C) Complicated methods
D) Low specificity

Question 36

Which bacterium does not cause fever?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori

Question 37

Which of the following illnesses is not caused by Streptococcus pyogenes directly,but rather by destructive host defense responses?

A) Pharyngitis
B) Pyoderma (impetigo)
C) Acute rheumatic fever
D) Scarlet fever

Question 38

The current standard method for diagnosing Rocky Mountain spotted fever is often unhelpful to the patient because:

A) it lacks sensitivity.
B) the diagnosis is obtained after the period in which treatment must begin.
C) the sampling procedure is very invasive.
D) it lacks specificity.

Question 39

Which organism is difficult to culture because it lacks a cell wall?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori

Question 40

Which microorganism is capable of causing life-threatening situations in which superantigens activate abnormally large numbers of T cells to release massive amounts of cytokines?

A) Streptococcus pyogenes
B) Mycoplasma pneumoniae
C) Rickettsia rickettsii
D) Helicobacter pylori