Staphylococcus aureus: Bacteriology and Pathogenesis
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Staphylococcus aureus: Bacteriology and Pathogenesis

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.

Created by
@EnthusiasticLapSteelGuitar

Questions and Answers

What is the characteristic of Staphylococcus aureus that allows it to inhibit complement activation and phagocytosis?

Production of protein A

Which of the following is NOT a common site of colonization by Staphylococcus aureus?

Small intestine

What is the mechanism of action of TSST-1 in toxic shock syndrome?

Binding to MHC II and T-cell receptor

What is the characteristic of Staphylococcal food poisoning?

<p>Short incubation period followed by nonbloody diarrhea and emesis</p> Signup and view all the answers

What is the effect of cooking on Staphylococcal enterotoxin?

<p>It is heat stable</p> Signup and view all the answers

Which gene is responsible for MRSA resistance by altering penicillin-binding proteins?

<p>mecA gene</p> Signup and view all the answers

What effect does Panton-Valentine leukocidin (PVL) have on leukocytes and tissues?

<p>Kills leukocytes and causes tissue necrosis</p> Signup and view all the answers

Why is penicillin generally not used to treat MRSA infections?

<p>Beta-lactam antibiotics have minimal efficacy against MRSA</p> Signup and view all the answers

Which of the following is NOT a recommended treatment option for MRSA infections?

<p>Nafcillin</p> Signup and view all the answers

What is a characteristic feature of MRSA that makes it a serious healthcare-associated infection?

<p>Its ability to alter penicillin-binding proteins</p> Signup and view all the answers

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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