Multiple Choice Questions (MCQs) on Acute Rheumatic Fever and Group A Streptococcus with Explanations: Medical microbiology

Multiple Choice Questions (MCQs) on Acute Rheumatic Fever and Group A Streptococcus with Explanations:

Question 1:

Acute Rheumatic Fever (ARF) is primarily caused by which bacterial species?

a) Staphylococcus aureus
b) Streptococcus pneumoniae
c) Streptococcus agalactiae
d) Streptococcus pyogenes (Group A Streptococcus)

Answer: d) Streptococcus pyogenes (Group A Streptococcus)

Explanation: ARF is primarily caused by Group A Streptococcus (S. pyogenes), particularly following untreated or inadequately treated streptococcal infections.

Question 2:

Which virulence factor of Streptococcus pyogenes plays a key role in the development of Acute Rheumatic Fever?

a) Capsule
b) Lipopolysaccharide (LPS)
c) M protein
d) Teichoic acid

Answer: c) M protein

Explanation: The M protein on the surface of Streptococcus pyogenes plays a crucial role in molecular mimicry, triggering the autoimmune response responsible for Acute Rheumatic Fever.

Question 3:

Molecular mimicry in Acute Rheumatic Fever refers to:

a) The ability of bacteria to mimic host cells.
b) The interaction between antibodies and antigens.
c) The cross-reactivity between bacterial antigens and host tissues.
d) The production of toxins by Streptococcus pyogenes.

Answer: c) The cross-reactivity between bacterial antigens and host tissues.

Explanation: Molecular mimicry involves the immune response mistaking bacterial antigens (such as M protein) for host antigens, leading to the autoimmune response seen in ARF.

Question 4:

Which of the following clinical manifestations is NOT a major criterion for diagnosing Acute Rheumatic Fever?

a) Carditis
b) Chorea
c) Elevated C-reactive protein
d) Subcutaneous nodules

Answer: c) Elevated C-reactive protein

Explanation: Elevated C-reactive protein is considered a minor criterion for diagnosing ARF, not a major criterion.

Question 5:

What is the primary treatment for Acute Rheumatic Fever to prevent complications and reduce the risk of spreading the infection?

a) Antiviral medications
b) Antibiotics, such as penicillin
c) Corticosteroids
d) Nonsteroidal anti-inflammatory drugs (NSAIDs)

Answer: b) Antibiotics, such as penicillin

Explanation: Early treatment with antibiotics, especially penicillin, helps eradicate remaining Streptococcus pyogenes bacteria and prevent complications like rheumatic heart disease.

Question 6:

Which laboratory test involves streaking a throat swab sample onto a selective agar plate to isolate S. pyogenes?

a) ELISA
b) Western blot
c) Throat swab culture
d) Polymerase chain reaction (PCR)

Answer: c) Throat swab culture

Explanation: Throat culture involves streaking the sample on agar plates to grow and isolate bacteria for identification, including Streptococcus pyogenes.

Question 7:

Which of the following tests helps differentiate Streptococcus pyogenes from other streptococcal species by its sensitivity to bacitracin?

a) Optochin test
b) Bacitracin test
c) Hippurate hydrolysis test
d) Catalase test

Answer: b) Bacitracin test

Explanation: The bacitracin sensitivity test helps differentiate Streptococcus pyogenes (sensitive) from other streptococcal species (resistant).

Question 8:

Which test detects the presence of Group A Streptococcus antigens and provides rapid results?

a) Throat swab culture
b) Gram staining
c) Rapid strep test
d) Catalase test

Answer: c) Rapid strep test

Explanation: The rapid strep test detects Group A Streptococcus antigens and provides quick results, often within minutes.

Question 9:

Which clinical manifestation of Acute Rheumatic Fever involves rapid, jerky movements and behavioral changes?

a) Carditis
b) Arthritis
c) Chorea
d) Subcutaneous nodules

Answer: c) Chorea

Explanation: Chorea is a neurological disorder characterized by rapid, jerky movements and behavioral changes, often seen in Acute Rheumatic Fever.

Question 10:

Which genetic marker can influence an individual's susceptibility to developing Acute Rheumatic Fever after a streptococcal infection?

a) HLA-B27
b) Rh factor
c) ABO blood type
d) Genetic markers associated with the immune response

Answer: d) Genetic markers associated with the immune response

Explanation: Genetic factors can influence an individual's susceptibility to ARF, particularly genetic markers associated with the immune response to bacterial antigens.

Question 11:

Which of the following is a major clinical manifestation of Acute Rheumatic Fever that involves inflammation of the heart?

a) Chorea
b) Arthritis
c) Carditis
d) Subcutaneous nodules

Answer: c) Carditis

Explanation: Carditis refers to inflammation of the heart and is a major clinical manifestation of Acute Rheumatic Fever.

Question 12:

Which bacterial virulence factor plays a crucial role in molecular mimicry and the development of Acute Rheumatic Fever?

a) Capsule
b) M protein
c) Lipopolysaccharide (LPS)
d) Teichoic acid

Answer: b) M protein

Explanation: The M protein of Streptococcus pyogenes is a key virulence factor that triggers molecular mimicry and leads to the autoimmune response in ARF.

Question 13:

What is the primary mode of transmission of Group A Streptococcus (Streptococcus pyogenes)?

a) Airborne droplets
b) Contaminated food
c) Fecal-oral route
d) Direct contact with respiratory secretions

Answer: d) Direct contact with respiratory secretions

Explanation: Group A Streptococcus is primarily transmitted through direct contact with respiratory secretions, such as coughing and sneezing.

Question 14:

Which of the following is NOT a potential complication of Acute Rheumatic Fever?

a) Rheumatic heart disease
b) Glomerulonephritis
c) Meningitis
d) Chorea

Answer: c) Meningitis

Explanation: While Acute Rheumatic Fever can lead to complications such as rheumatic heart disease, glomerulonephritis, and chorea, it is not directly associated with meningitis.

Question 15:

Which laboratory test involves adding hydrogen peroxide to a bacterial colony to determine its catalase activity?

a) Coagulase test
b) Oxidase test
c) Bacitracin test
d) Catalase test

Answer: d) Catalase test

Explanation: The catalase test is used to determine the presence of catalase enzyme in bacteria by observing the production of bubbles (effervescence) upon adding hydrogen peroxide.

Question 16:

Which of the following is a minor criterion for diagnosing Acute Rheumatic Fever?

a) Carditis
b) Arthritis
c) Elevated erythrocyte count
d) Subcutaneous nodules

Answer: b) Arthritis

Explanation: Arthritis is a minor criterion for diagnosing Acute Rheumatic Fever, characterized by joint inflammation without infection.

Question 17:

What is the gold standard for diagnosing Group A Streptococcus infection in the laboratory?

a) Rapid strep test
b) Gram staining
c) Throat culture
d) Molecular PCR test

Answer: c) Throat culture

Explanation: Throat culture is considered the gold standard for diagnosing Group A Streptococcus infection in the laboratory.

Question 18:

Which genetic factor can increase an individual's susceptibility to developing Acute Rheumatic Fever after a streptococcal infection?

a) Rh factor
b) ABO blood type
c) HLA-B27
d) Genetic markers associated with streptococcal antigens

Answer: d) Genetic markers associated with streptococcal antigens

Explanation: Genetic markers associated with streptococcal antigens can influence an individual's susceptibility to Acute Rheumatic Fever.

Question 19:

Which of the following medications is NOT commonly used in the treatment of Acute Rheumatic Fever?

a) Penicillin
b) Nonsteroidal anti-inflammatory drugs (NSAIDs)
c) Corticosteroids
d) Antibiotics targeting Gram-negative bacteria

Answer: d) Antibiotics targeting Gram-negative bacteria

Explanation: Antibiotics targeting Gram-negative bacteria are not commonly used in the treatment of Acute Rheumatic Fever. Penicillin is the preferred antibiotic.

Question 20:

Which of the following tests detects the presence of specific Group A Streptococcus antigens and provides rapid results?

a) Catalase test
b) Throat culture
c) Rapid strep test
d) Gram staining

Answer: c) Rapid strep test

Explanation: The rapid strep test detects specific Group A Streptococcus antigens and provides quick results, often within minutes.             

Question 21:
 Rheumatic fever primarily affects which of the following body systems?

a) Digestive system
b) Musculoskeletal system
c) Respiratory system
d) Nervous system

Answer: b) Musculoskeletal system

Explanation: Rheumatic fever primarily affects the musculoskeletal system, leading to symptoms such as joint pain and swelling, a characteristic feature of the disease.

Question 22:

 Which of the following is the characteristic feature of rheumatic fever?
a) Joint pain and swelling
b) Skin rash
c) Heart murmurs
d) All of the above

Answer: d) All of the above

Explanation: Rheumatic fever is characterized by joint pain and swelling (arthritis), skin rash, and heart murmurs due to inflammation of the heart valves.

Question 23: 

Which of the following age groups are at higher risk for rheumatic fever?
Select the correct answer
a) Adults 50 and above
b) Children ages 5-15
c) Infants
d) Women ages 20-40
 

Answer: b) Children ages 5-15

Explanation: Rheumatic fever is more common in children ages 5-15, particularly after an untreated or inadequately treated streptococcal infection.

Question 24:  

The best way to prevent rheumatic fever is:
a) Avoiding contact with infected individuals
b) Getting vaccinated
c) Early diagnosis and treatment of streptococcal infections
d) Washing hands frequently

Answer: c) Early diagnosis and treatment of streptococcal infections

Explanation: The best way to prevent rheumatic fever is by promptly diagnosing and treating streptococcal infections with antibiotics to prevent complications.

Question 25: 

Rheumatic fever can lead to long-term complications, primarily affecting the................................
a) Heart
b) Kidneys
c) Liver
d) Lungs

Answer: a) Heart

Explanation: Rheumatic fever can lead to long-term complications that primarily affect the heart, leading to rheumatic heart disease and damage to the heart valves.

Question 26:

The condition characterized by scarring and damage to the heart valves as a consequence of rheumatic fever is called............................................
a) Coronary artery disease
b) Rheumatic heart disease
c) Rheumatoid arthritis
d) Septicemia

Answer: b) Rheumatic heart disease

Explanation: Rheumatic heart disease is the condition characterized by scarring and damage to the heart valves as a consequence of rheumatic fever.

Question 27: 

What is the primary symptom of rheumatic heart disease?
a) Chest pain and shortness of breath
b) Cough
c) Painful urination
d) Red eyes

Answer: a) Chest pain and shortness of breath

Explanation: The primary symptom of rheumatic heart disease is chest pain and shortness of breath, often due to the impact of damaged heart valves on cardiac function.

B. Acute Rheumatic Fever and Group A Streptococcus

Acute Rheumatic Fever (ARF) is an inflammatory condition that can develop after a streptococcal throat infection, particularly caused by Group A Streptococcus (GAS) bacteria, specifically Streptococcus pyogenes. The microbiological aspects of ARF involve the interaction between the bacterial infection and the immune response, leading to the autoimmune response responsible for the inflammation and tissue damage seen in this condition.

Streptococcus pyogenes Infection:

ARF often develops as a result of an untreated or inadequately treated infection with Group A Streptococcus bacteria. These bacteria are known to produce several virulence factors that contribute to their ability to colonize and cause infections in the human body. One of the most important virulence factors is the M protein, which helps the bacteria evade the host immune response and plays a role in molecular mimicry that triggers autoimmunity in ARF.

Molecular Mimicry and Autoimmunity:

In ARF, the immune system's response to the streptococcal infection can cross-react with host tissues, especially heart valves and joints. This phenomenon is attributed to molecular mimicry, where certain bacterial antigens share structural similarities with host antigens. The M protein of Streptococcus pyogenes is a major contributor to molecular mimicry. Antibodies produced against the M protein can mistakenly target host tissues, leading to inflammation and tissue damage.

Immune Response and Pathogenesis:

Upon infection with Streptococcus pyogenes, the immune system mounts a response to eliminate the bacteria. However, in some individuals, the immune response becomes dysregulated and starts attacking host tissues due to molecular mimicry. This immune response targets not only the bacteria but also normal host tissues, particularly heart valves and joints. This results in inflammation, tissue damage, and the clinical manifestations characteristic of ARF.

Role of Genetic Factors:

Genetic factors can also influence an individual's susceptibility to developing ARF after a streptococcal infection. Genetic predisposition may affect the immune response, making certain individuals more prone to developing the autoimmune reaction responsible for ARF.

Diagnosis of Group A Streptococcus

Diagnosing ARF involves considering both clinical and laboratory criteria. The Jones criteria are commonly used for diagnosis:

Major Criteria:

• Carditis: Inflammation of the heart, often presenting as a new heart murmur, tachycardia, and other signs of heart involvement.
• Polyarthritis: Inflammation of multiple joints, usually involving large joints such as knees, ankles, elbows, and wrists.
• Chorea: A neurological disorder characterized by rapid, jerky movements and behavioral changes.
• Subcutaneous nodules: Painful, firm lumps under the skin, typically over bony prominences.

Minor Criteria:

• Fever: Elevated body temperature during the acute phase.
• Arthralgia: Joint pain without inflammation.
• Elevated acute-phase reactants: Increased levels of markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).
• Prolonged PR interval on ECG: Indicative of heart involvement.
• Diagnosis is Confirmed if:
• Two major criteria, or
• One major and two minor criteria are present, along with evidence of a preceding streptococcal infection.

Laboratory Tests:

• Throat swab for GAS culture or rapid antigen detection test to confirm a recent streptococcal infection.
• Blood tests for elevated acute-phase reactants (CRP, ESR).
• Electrocardiogram (ECG) to assess for heart involvement.
• Echocardiogram to evaluate heart valve function and inflammation.

Identification of Group A Streptococcus (Streptococcus pyogenes): Step-by-Step Procedure

The identification of Group A Streptococcus (GAS), also known as Streptococcus pyogenes, involves a series of laboratory tests to accurately confirm the presence of this bacterium. Here is a step-by-step procedure for identifying GAS:

1. Sample Collection:

Collect a throat swab sample from the patient suspected of having a streptococcal infection. Ensure that the swab touches the back of the throat and tonsils to collect a sufficient amount of bacterial material.

2. Inoculation:

Streak the collected sample onto a selective agar plate, such as a blood agar plate or a selective medium specifically designed for streptococci.

3. Incubation:

Place the inoculated agar plate in an incubator at an appropriate temperature (usually 35-37°C) and allow the bacteria to grow for 24-48 hours.

4. Colony Morphology:

Examine the grown colonies for their morphological characteristics. GAS colonies typically exhibit the following features:

Small to medium-sized colonies.

Beta-hemolysis on blood agar, which means a clear zone of complete hemolysis around the colony.

Grayish-white or translucent appearance.

5. Gram Staining:

Perform a Gram stain on representative colonies to observe their Gram staining characteristics. GAS should appear as Gram-positive cocci in chains.

6. Catalase Test:

Perform a catalase test by adding hydrogen peroxide (H2O2) to a colony. GAS is catalase-negative, so it will not produce bubbles or effervescence in response to hydrogen peroxide.

7. Bacitracin Sensitivity Test:

Place a bacitracin disk on the surface of the agar plate. Incubate the plate and observe for the zone of inhibition around the disk. GAS is sensitive to bacitracin, so a clear zone of inhibition will be present around the disk.

8. Hippurate Hydrolysis Test:

Inoculate a hippurate agar slant with a pure culture of the isolate. After incubation, add ninhydrin reagent. A positive reaction (blue color development) indicates the presence of GAS.

9. PYR (L-pyrrolidonyl-β-naphthylamide) Test:

Streak the bacterial isolate on a PYR agar plate. Incubate and then add PYR reagent. Positive reaction (cherry-red color development) indicates the presence of GAS.

10. Serological Testing (Optional):

While the above tests are often sufficient to identify GAS, serological tests such as the Lancefield grouping test can further confirm the strain's identity.

11. Molecular Identification (Optional):

Molecular techniques, such as PCR targeting specific GAS genes, can provide rapid and accurate identification of GAS.

12. Confirmation:

Based on the results of colony morphology, Gram staining, catalase test, bacitracin sensitivity, and other relevant tests, confirm the identification of Group A Streptococcus.