SEROLOGICAL DIAGNOSIS OF INFECTIOUS DISEASES (Bacterial infections) Flashcards
memorization
1
Q
Test principle of Weil Felix reaction:
A
Direct agglutination
2
Q
Weil Felix reaction is a febrile test that is based on the cross-reaction of _________________ produced in response to rickettsial infection, with antigens in the three strains of proteus
A
Weil Felix reaction is a febrile test that is based on the cross-reaction of HETEROPHILE ANTIBODIES produced in response to rickettsial infection, with antigens in the three strains of proteus
3
Q
Three (3) strains of Proteus used in the Weil-Felix reaction:
A
- OX-2 - P. vulgaris
- OX-19 - P. vulgaris
- OX-K - P. mirabilis
4
Q
Reporting of Weil-Felix reaction:
- Titer of 1:80 = ??
- Titer of 1:160 = ??
A
Reporting of Weil-Felix reaction:
- Titer of 1:80 = SUSPICIOUS/SUSPECTED
- Titer of 1:160 = INDICATIVE
5
Q
Typica; Weil Felix reactions
Disease: Epidemic typhus
Organism: R. prowazekii
OX-19: ?
OX-2: ?
OX-K: ?
A
Typica; Weil Felix reactions
Disease: Epidemic typhus
Organism: R. prowazekii
OX-19: 4+
OX-2: +
OX-K: 0
6
Q
Typical Weil Felix reactions
Disease: Murine typhus
Organism: R. typhi
OX-19: ?
OX-2: ?
OX-K: ?
A
Typical Weil Felix reactions
Disease: Murine typhus
Organism: R. typhi
OX-19: 4+
OX-2: +
OX-K: 0
7
Q
Typical Weil Felix reactions
Disease: Scrub typhus
Organism: R. tsutsugamushi
OX-19: ?
OX-2: ?
OX-K: ?
A
Typical Weil Felix reactions
Disease: Scrub typhus
Organism: R. tsutsugamushi
OX-19: 0
OX-2: 0
OX-K: 2+
8
Q
Strep throat can lead to complications like:
A
- Rheumatic Heart disease
- Acute glomerulonephritis
9
Q
Strep skin infection can lead to:
A
- Acute glomerulonephritis only
(not RHD)
10
Q
Virulence factor of S. pyogenes that is anti-phagocytic, and mimics the protein of the heart valves. it is associated with strains that cause rheumatic fever:
A
M protein
11
Q
Difference between Streptolysin O and S
A
Streptolysin O
- Oxygen labile
- immunogenic
Streptolysin S
- Oxygen stable
- Non-immunogenic
12
Q
Spreading factor of S. pyogenes:
A
Hyaluronidase
13
Q
Virulence factor of S. pyogenes responsible for red rash in scarlet fever:
A
Erythrogenic toxin
14
Q
Anti-streptolysin O titration test is based on the ___________ of the hemolytic activity of streptolysin O
A
NEUTRALIZATION
15
Q
Anti-streptolysin O titration test
Positive result:
Negative result:
A
Anti-streptolysin O titration test
Positive result: NO HEMOLYSIS (Ab is present)
Negative result: HEMOLYSIS (Ab is absent)
16
Q
Anti-streptolysin O titration test
Normal titer: ____ Todd units
Considered moderately elevated if the titer is:
Adult: ____ Todd units
Child: _____ Todd units
A
Anti-streptolysin O titration test
Normal titer:
- 166 Todd unit or below
Considered moderately elevated if the titer is:
Adult: 240 Todd units
Child: 320 Todd units
17
Q
A particle agglutination test in which erythrocytes are coated with a crude mixture of streptococcal antigens so that antibodies to any of the streptococcal antigens can be detected:
A
Multienzyme test/ Streptozyme
18
Q
Diagnosis of recent streptococcal infections; useful in detecting streptococcal skin infection
A
Streptococcal anti-DNAse B determination
NOTE: Sensitivity is increased for the detection of glomerulonephritis preceded by streptococcal skin infections as ASO antibodies are not stimulated by this type of disease
19
Q
A susceptibility test for streptococcal infection:
A
Dick’s test
20
Q
A diagnostic test for streptococcal infection:
A
Schultz Charlton test
21
Q
The most reliable indicator of Brucella infection is the _____ test:
A
Agglutination test
22
Q
Method of choice for H. pylori Ab detection:
A
ELISA (Enzyme-Linked Immunosorbent Assay)
23
Q
What immunoglobulin is the primary antibody present and detected by serological methods since most infections have become chronic before diagnosis?
A
IgG antibody
24
Q
Chronic inflammatory disease primarily affecting joints and joint tissues; most common autoimmune disease:
A
Rheumatoid Arthritis
25
Rheumatoid factor:
IgM with specificity toward the Fc portion of IgG
26
Proinflammatory cytokines of rheumatoid arthritis in synovial fluid:
IL-1, 6, 8, 15, 18, TNF-a
27
Serological testing for rheumatoid arthritis
Rapid Latex Agglutination
(Principle: Passive Agglutination)
28
Significant titer for Rheumatoid Arthritis
Positive titer:
Weakly positive:
Negative:
Significant titer for Rheumatoid Arthritis (memorize!!!)
Positive titer: Greater than or equal to 80
Weakly positive: 20-40
Negative: 1:20
29
Most widely used marker of inflammation; abnormal protein that appears in the acute stages of various inflammatory disorders
C-reactive protein (CRP)
30
All of the following are protective mechanisms against bacteria except
a. production of antimicrobial defense peptides.
b. phagocytosis.
c. activation of complement.
d. release of lipid A from the bacterial cell.
d. Release of lipid A from the bacterial cell.
Protective Mechanisms Against Bacteria:
1. Production of antimicrobial defense peptides (a): Interferes with bacterial cell membranes.
2. Phagocytosis (b): Engulfs and destroys bacteria.
3. Activation of complement (c): Enhances phagocytosis, lysis, and inflammation.
Lipid A:
1. Component of Gram-negative bacterial LPS (lipopolysaccharides).
2. Induces inflammatory responses.
3. Not a protective mechanism.
Other protective mechanisms:
1. Antibody-mediated immunity
2. Cell-mediated immunity
3. Inflammatory responses
4. Antimicrobial enzymes (e.g., lysozyme)
31
All of the following are characteristics of streptococcal M protein except
a. It is the chief virulence factor of Group A streptococci.
b. It provokes an immune response.
c. Antibodies to one serotype protect against other serotypes.
d. It limits phagocytosis of the organism.
c. Antibodies to one serotype protect against other serotypes.
Characteristics of Streptococcal M Protein:
1. Chief virulence factor of Group A Streptococci (GAS) (a).
2. Provokes immune response, inducing specific antibodies (b).
3. Inhibits phagocytosis by binding complement-regulating proteins (d).
M Protein Limitations:
1. Over 200 serotypes, with limited cross-protection.
2. Antibodies against one serotype typically don't protect against others.
Functions:
1. Adhesion
2. Invasion
3. Immune evasion
4. Complement regulation
32
An ASO titer and a streptozyme test are performed on a patient’s serum. The ASO titer is negative, the streptozyme test is positive, and both the positive and negative controls react appropriately. What can you conclude from these test results?
a. The ASO is falsely negative.
b. The patient has an antibody to a streptococcal exoenzyme other than streptolysin O.
c. The patient has not had a previous streptococcal infection.
d. The patient has scarlet fever.
b. The patient has an antibody to a streptococcal exoenzyme other than streptolysin O.
Explanation:
Test Results Interpretation
1. ASO (Antistreptolysin O) titer negative: Indicates no antibodies against streptolysin O, a streptococcal toxin.
2. Streptozyme test positive: Detects antibodies against multiple streptococcal antigens, including streptolysin O, streptokinase, and others.
Conclusion
1. The positive Streptozyme test suggests antibodies against streptococcal antigens other than streptolysin O.
2. This indicates previous exposure or infection with Group A beta-hemolytic streptococci (GABHS).
Options Analysis
1. a. ASO falsely negative: Unlikely, given proper controls.
2. c. No previous streptococcal infection: Contradicted by positive Streptozyme test.
3. d. Scarlet fever: Cannot be confirmed solely by these tests.
33
Which of the following applies to acute rheumatic fever?
a. Symptoms begin after S. pyogenes infection of the throat or the skin.
b. Antibodies to Group A streptococci are believed to cross-react with heart tissue.
c. Diagnosis is usually made by culture of the organism.
d. All patients suffer permanent disability.
b. Antibodies to Group A streptococci are believed to cross-react with heart tissue.
This option directly addresses the pathophysiological mechanism underlying acute rheumatic fever (ARF), making it the most accurate choice.
34
Which of the following indicates the presence of anti-DNase B activity in serum?
a. Reduction of methyl green from green to colorless
b. Clot formation when acetic acid is added
c. Inhibition of red blood cell hemolysis
d. Lack of change in the color indicator
d. Lack of change in the color indicator.
The anti-DNase B test measures the ability of antibodies to neutralize DNase B enzyme activity. A lack of color change indicates anti-DNase B activity, as the enzyme's activity is inhibited.
35
Which of the following is considered to be a nonsuppurative complication of streptococcal infection?
a. Acute rheumatic fever
b. Scarlet fever
c. Impetigo
d. Pharyngitis
a. Acute rheumatic fever.
Nonsuppurative complications of streptococcal infections are characterized by inflammation without pus formation. Acute rheumatic fever (ARF) is a classic example, involving:
Major Criteria
1. Carditis
2. Polyarthritis
3. Chorea
4. Erythema marginatum
5. Subcutaneous nodules
Minor Criteria
1. Fever
2. Arthralgia
3. Elevated CRP/ESR
Other options are suppurative (pus-forming) complications:
b. Scarlet fever (rash with pus-filled lesions)
c. Impetigo (skin infection with pus)
d. Pharyngitis (throat infection, potentially suppurative)
36
All of the following are ways that bacteria can evade host defenses except
a. presence of a capsule.
b. stimulation of chemotaxis.
c. production of toxins.
d. lack of adhesion to phagocytic cells.
b. Stimulation of chemotaxis.
Bacteria evade host defenses by:
1. Presence of a capsule (a): Interferes with phagocytosis.
2. Production of toxins (c): Damages host tissues.
3. Lack of adhesion to phagocytic cells (d): Evades phagocytosis.
Stimulation of chemotaxis (b) actually enhances host defense:
1. Attracts immune cells (neutrophils, macrophages) to infection sites.
2. Facilitates phagocytosis.
Other evasion strategies:
1. Biofilm formation
2. Antigenic variation
3. Immune suppression
4. Intracellular survival
37
Antibody testing for Rocky Mountain spotted fever may not be helpful for which reason?
a. It is not specific.
b. It is too complicated to perform.
c. It is difficult to obtain a blood specimen.
d. Antibody production takes at least a week before detection.
d. Antibody production takes at least a week before detection.
Antibody testing for Rocky Mountain spotted fever (RMSF) may not be helpful initially because:
Early Limitations
1. Delayed antibody response: IgM antibodies typically appear 7-10 days post-infection.
2. Window period: Early testing may yield false negatives.
Diagnostic Challenges
1. Symptoms resemble other tick-borne illnesses.
2. Rapid diagnosis is essential due to high mortality rate.
Alternative Diagnostic Approaches
1. Clinical presentation and medical history.
2. PCR (polymerase chain reaction) testing.
3. Immunohistochemistry.
4. Direct fluorescent antibody staining.
38
Which of the following enzymes is used to detect the presence of H. pylori infections?
a. DNase
b. Hyaluronidase
c. Urease
d. Peptidase
c. Urease.
Helicobacter pylori (H. pylori) produces urease, which breaks down urea into ammonia and carbon dioxide. Diagnostic tests exploit this enzyme:
Diagnostic Tests
1. Rapid Urease Test (RUT): Gastric biopsy sample turns pink/red due to pH change.
2. Urea Breath Test (UBT): Inhaling labeled urea; breath analysis detects labeled carbon dioxide.
3. Stool Antigen Test: Detects urease activity.
Urease is essential for H. pylori's survival, helping neutralize stomach acid.
Other options:
a. DNase: Associated with Streptococcus pyogenes.
b. Hyaluronidase: Found in various bacteria, including Staphylococcus aureus.
d. Peptidase: Enzyme with broad bacterial distribution.
39
Which of the following reasons make serological identification of a current infection with
Helicobacter pylori difficult?
a. No antibodies appear in the blood.
b. Only IgM is produced.
c. Antibodies remain after initial treatment.
d. No ELISA tests have been developed.
c. Antibodies remain after initial treatment.
Serological identification of current Helicobacter pylori infection is challenging due to:
Persistence of Antibodies
1. IgG antibodies remain detectable for months/years after successful treatment.
2. IgA antibodies can persist for several months.
Other Limitations
1. Window period: IgM and IgG antibodies may not be detectable early in infection.
2. Variability: Antibody responses differ among individuals.
3. Cross-reactivity: Potential false positives due to other bacterial infections.
Diagnostic Alternatives
1. Urease breath test (UBT)
2. Stool antigen test
3. Endoscopy with biopsy
4. PCR (polymerase chain reaction)
Incorrect Options
1. a. Antibodies do appear in the blood.
2. b. Both IgM (acute) and IgG (chronic) antibodies are produced.
3. d. ELISA tests are available but have limitations.
40
M. pneumoniae infections are associated with the production of which antibodies?
a. Cold agglutinins
b. Antibodies to ATPase
c. Antibodies to DNase
d. Antibodies to Proteus bacteria
a. Cold agglutinins.
Mycoplasma pneumoniae infections trigger production of:
Cold Agglutinins
1. IgM antibodies
2. Autoantibodies targeting red blood cell antigens (I/i antigens)
3. Cause hemolysis (red blood cell destruction) at temperatures below 37°C (98.6°F)
Other options:
b. Antibodies to ATPase: Associated with Streptococcus infections.
c. Antibodies to DNase: Linked to Streptococcal infections.
d. Antibodies to Proteus bacteria: Related to Proteus infections, not M. pneumoniae.
M. pneumoniae infections often present with:
1. Respiratory symptoms (pneumonia, bronchitis)
2. Fever
3. Headache
4. Fatigue
41
Which of the following best describes the principle of the IFA test for detection of antibodies produced in Rocky Mountain spotted fever?
a. Patient serum is applied to a microtiter plate coated with a monoclonal antibody directed against the target antigen. A detection antibody labeled with biotin and directed against the target antigen is added. After addition of a substrate, a color reaction develops, indicating presence of the antigen.
b. Specific antibodies in the serum sample attach to the antigens fixed to a microscope slide. In a second step, the attached antibodies are stained with fluorescein-labeled antihuman immunoglobulin and visualized with a fluorescence microscope.
c. The serum sample is treated chemically to link the target antibodies to a fluorophore. The labeled sample is applied to a microscope slide to which the antigen has been
attached. Following a wash step, the slide is examined for fluorescence.
d. Patient serum is applied to a slide to which a specific antigen is bound. Following a wash step, a chromogenic dye is applied that binds to the Fc region of IgG and IgM antibodies. After a second wash step, the slide is examined for fluorescence
b. Specific antibodies in the serum sample attach to the antigens fixed to a microscope slide. In a second step, the attached antibodies are stained with fluorescein-labeled anti-human immunoglobulin and visualized with a fluorescence microscope.
This describes the Indirect Fluorescence Antibody (IFA) test principle:
Key Steps
1. Antigen preparation: Rocky Mountain spotted fever (RMSF) antigens are fixed on a microscope slide.
2. Serum application: Patient serum (containing potential RMSF antibodies) is applied.
3. Antibody binding: Specific antibodies bind to RMSF antigens.
4. Fluorescent labeling: Fluorescein-labeled anti-human immunoglobulin (Ig) binds to attached antibodies.
5. Visualization: Fluorescence microscopy detects bound antibodies.
Advantages
1. High sensitivity
2. Specificity
3. Rapid results
Limitations
1. Requires specialized equipment
2. Subjective interpretation
3. Potential cross-reactivity
42
Which of the following is true regarding exotoxins and endotoxins?
a. Both endotoxins and exotoxins are highly immunogenic, allowing for the development of protective antibodies and vaccines.
b. Endotoxins have targeted activity, whereas exotoxins have systemic effects when released.
c. Endotoxins are released from the cell wall of dead bacteria, whereas exotoxins are released from live bacteria.
d. Both endotoxins and exotoxins bind to specific receptors on a bacterial cell, leading to cell lysis.
c. Endotoxins are released from the cell wall of dead bacteria, whereas exotoxins are released from live bacteria.
Key differences:
Exotoxins
1. Protein-based: Highly potent, soluble proteins.
2. Released by live bacteria: Secreted through bacterial membranes.
3. Specific targets: Bind to specific receptors, causing localized damage.
4. Highly immunogenic: Stimulate protective antibody responses.
5. Examples: Botulinum toxin, Tetanus toxin, Diphtheria toxin.
Endotoxins
1. Lipopolysaccharide-based: Component of Gram-negative bacterial cell walls.
2. Released by dead bacteria: Liberated during cell lysis.
3. Systemic effects: Trigger inflammatory responses, causing fever, shock, and organ damage.
4. Less immunogenic: Weaker antibody responses compared to exotoxins.
5. Examples: Lipopolysaccharides from E. coli, Salmonella, and Shigella.
43
Characteristics of a bacterial capsule include which of the following?
a. It cannot be used for vaccine development.
b. It is composed of peptidoglycan.
c. It is an important mechanism for protecting a bacterium against ingestion by polymorphonuclear leukocytes PMNs.
d. It is what causes bacteria to stain as gram-negative.
c. It is an important mechanism for protecting a bacterium against ingestion by polymorphonuclear leukocytes (PMNs).
Bacterial capsule characteristics:
1. Composed of polysaccharides (e.g., capsular polysaccharides).
2. Protects bacteria from phagocytosis (ingestion) by PMNs and macrophages.
3. Virulence factor: Enhances bacterial pathogenicity.
4. Antigenic: Stimulates immune responses.
5. Vaccine target: Capsular polysaccharides are used in vaccines (e.g., pneumococcal, meningococcal).
Incorrect options:
a. Capsular polysaccharides are used in vaccine development.
b. Peptidoglycan forms the bacterial cell wall, not the capsule.
d. Gram staining depends on cell wall composition (peptidoglycan and lipopolysaccharides), not the capsule.
Examples of encapsulated bacteria:
1. Streptococcus pneumoniae
2. Haemophilus influenzae
3. Neisseria meningitidis
4. Klebsiella pneumoniae
44
Which of the following statements regarding Helicobacter pylori is not true?
a. It is associated with an increased risk of gastric carcinoma.
b. It is the cause of most cases of acute food poisoning in the United States.
c. It is a major cause of peptic ulcers in the United States.
d. It is positive for urease
b. It is the cause of most cases of acute food poisoning in the United States.
Helicobacter pylori (H. pylori) facts:
1. Associated with increased risk of gastric carcinoma (a).
2. Major cause of peptic ulcers (c).
3. Positive for urease (d), enabling diagnosis via urea breath test.
However, H. pylori is not typically associated with acute food poisoning. Common foodborne pathogens in the US include:
1. Norovirus
2. Salmonella
3. Escherichia coli (E. coli)
4. Campylobacter
5. Staphylococcus aureus
