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Questions and Answers
What is the characteristic of Staphylococcus aureus that allows it to inhibit complement activation and phagocytosis?
Which of the following is NOT a common site of colonization by Staphylococcus aureus?
What is the mechanism of action of TSST-1 in toxic shock syndrome?
What is the characteristic of Staphylococcal food poisoning?
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What is the effect of cooking on Staphylococcal enterotoxin?
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Which gene is responsible for MRSA resistance by altering penicillin-binding proteins?
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What effect does Panton-Valentine leukocidin (PVL) have on leukocytes and tissues?
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Why is penicillin generally not used to treat MRSA infections?
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Which of the following is NOT a recommended treatment option for MRSA infections?
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What is a characteristic feature of MRSA that makes it a serious healthcare-associated infection?
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Study Notes
Staphylococcus aureus Characteristics
- Gram-Positive, β-hemolytic, catalase-Positive, coagulase-Positive cocci in clusters
- Ferments mannitol
- Produces coagulase and toxins
- Forms a fibrin clot around itself, leading to an abscess
Virulence Factors
- Protein A, binds Fc-IgG, inhibiting complement activation and phagocytosis
Common Sites of Colonization
- Naress, ears, axilla, and groin
Presentations
- Inflammatory disease:
- Localized infections: skin infections (impetigo, cellulitis, folliculitis, furuncles, carbuncles), organ abscesses, pneumonia, endocarditis, septic arthritis, and osteomyelitis
- Systemic infections: infective endocarditis, meningitis, osteomyelitis, septic arthritis
- Toxin-mediated disease:
- Toxic shock syndrome (due to TSST-1)
- Scalded skin syndrome (due to exfoliative toxin)
- Rapid-onset food poisoning (due to enterotoxins)
Toxic Shock Syndrome (TSS)
- Caused by TSST-1, a superantigen that binds to MHCII and T-cell receptor
- Results in polyclonal T-cell activation and cytokine release
- Associated with prolonged use of vaginal tampons, nasal packing, or trauma surgery
- Symptoms: fever, vomiting, diarrhea, rash, desquamation, shock, and end-organ failure
- Laboratory results: increased AST, increased ALT, increased bilirubin
Staphylococcal Food Poisoning
- Due to ingestion of preformed toxin
- Results in short incubation period (2-6 hours) followed by non-bloody diarrhea and emesis
- Enterotoxin is heat stable and not destroyed by cooking
Antibiotic Resistance
- MRSA (methicillin-resistant S aureus): important cause of serious healthcare-associated and community-acquired infections
- Resistance due to altered penicillin-binding proteins (conferred by mecA gene)
- Treatment: Vancomycin, Aminoglycoside (e.g., Gentamicin), Clindamycin, TMP/SMX (Cotrimoxazole or Bactrim), or Linezolid
Treatment Options
- For MSSA (Methicillin-sensitive S aureus): Methicillin, Nafacillin, Dicloxacillin, and Oxacillin
- For MRSA (methicillin-resistant S aureus): Vancomycin, Aminoglycoside (e.g., Gentamicin), Clindamycin, TMP/SMX (Cotrimoxazole or Bactrim), or Linezolid
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Description
This quiz covers the characteristics, virulence factors, and presentations of Staphylococcus aureus, a gram-positive bacterium that causes various infections. Learn about its bacteriology and pathogenesis.
