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

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Questions and Answers

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

  • Production of protein A (correct)
  • Production of fibrin clot
  • Production of exfoliative toxin
  • Production of coagulase
  • Which of the following is NOT a common site of colonization by Staphylococcus aureus?

  • Ears
  • Axilla
  • Nares
  • Small intestine (correct)
  • What is the mechanism of action of TSST-1 in toxic shock syndrome?

  • Binding to MHC I and B-cell receptor
  • Binding to MHC II and T-cell receptor (correct)
  • Producing exfoliative toxin
  • Inhibiting complement activation
  • 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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    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.

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