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Questions and Answers
Which of the following is NOT a predisposing factor for infections caused by Staphylococcus aureus?
Which of the following is NOT a predisposing factor for infections caused by Staphylococcus aureus?
What key characteristic differentiates Staphylococcus aureus from other staphylococci?
What key characteristic differentiates Staphylococcus aureus from other staphylococci?
What is the common source of enterotoxins A-E that leads to gastroenteritis caused by Staphylococcus aureus?
What is the common source of enterotoxins A-E that leads to gastroenteritis caused by Staphylococcus aureus?
Which syndrome is associated with prolonged use of vaginal tampons or nasal packing due to Staphylococcus aureus?
Which syndrome is associated with prolonged use of vaginal tampons or nasal packing due to Staphylococcus aureus?
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Which of the following symptoms is associated with the gastroenteritis caused by Staphylococcus aureus?
Which of the following symptoms is associated with the gastroenteritis caused by Staphylococcus aureus?
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What is the primary mechanism of action of TSST-1 that leads to T-cell activation?
What is the primary mechanism of action of TSST-1 that leads to T-cell activation?
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Which of the following symptoms is commonly associated with osteomyelitis?
Which of the following symptoms is commonly associated with osteomyelitis?
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What is a distinguishing feature of secondary bacterial pneumonia after influenza?
What is a distinguishing feature of secondary bacterial pneumonia after influenza?
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Scalded Skin Syndrome is primarily caused by which of the following mechanisms?
Scalded Skin Syndrome is primarily caused by which of the following mechanisms?
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What is a significant characteristic of MRSA in the context of antibiotic resistance?
What is a significant characteristic of MRSA in the context of antibiotic resistance?
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Study Notes
Staphylococcus aureus
- Reservoir: Usually part of normal flora, commonly inhabiting nasal mucosa, ears, axilla, and groin. Around 25% of the population are carriers.
- Transmission: Primarily via hands, sneezing, surgical wounds, and contaminated food, including custard pastries, potato salad, and canned meats.
- Predisposing Factors for Infection: Predisposed by surgery/wounds, foreign bodies (tampons, surgical packing, sutures), severe neutropenia, IV drug abuse, chronic granulomatous disease, and Cystic Fibrosis.
- Pathogenesis: Contains Protein A in the peptidoglycan cell wall that binds to the Fc component of IgG, inhibiting complement activation and phagocytosis.
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Diseases and Pathogenicity:
Gastroenteritis
- Clinical Symptoms: Rapid onset (2-6 hours) of nausea, abdominal pain, vomiting, followed by watery diarrhea after ingesting toxin.
- Pathogenesis: Ingestion of preformed enterotoxins A-E in contaminated food (like custard pastries, mayonnaise, potato salad, canned meats). Enterotoxins are heat stable, fast acting, and decrease sodium and water absorption from the intestines.
Acute Infective Endocarditis
- Clinical Symptoms: Typically right-sided heart infection of the tricuspid valve, even if normal. Symptoms include fever, malaise, leukocytosis, and heart murmur (may be absent initially).
- Pathogenesis: Fibrin platelet mesh formation and cytolytic toxins, including Panton-Valentine leucocidin (PVL), form pores in infected cells and is acquired by bacteriophage.
Staphylococcal Toxic Shock Syndrome
- Clinical Symptoms: Characterized by fever, vomiting, rash, desquamation, shock, and end-organ failure. Increased AST, ALT, and bilirubin levels.
- Pathogenesis: Associated with prolonged use of vaginal tampons or nasal packing. TSST-1, a superantigen toxin, binds non-specifically to MHC class II on APCs and T-cell receptors (TCR) by cross-linking TCR's beta regions to MHC-II outside the antigen binding site. This leads to overwhelming polyclonal T-cell activation and, ultimately, a cytokine storm (IL-1, IL-2, IFN-γ, and TNF-α) causing shock.
Osteomyelitis
- Clinical Symptoms: Bone pain, fever, tissue swelling, redness, and lytic bone lesions on imaging.
- Pathogenesis: Cytolysin toxin and coagulase+, converts fibrinogen to fibrin clot, forming localized boils.
Pneumonia (Secondary bacterial pneumonia)
- Clinical Symptoms: Often follows influenza infection, especially in school-aged children. Presents with productive pneumonia, rapid onset, high necrosis rate, and high fatality. Characterized by salmon-colored sputum.
- Pathogenesis: Commonly occurs in patients with nosocomial infections, ventilator use, post-influenza, IV drug abuse, cystic fibrosis, CGD, etc.
Abscesses and Mastitis
- Clinical Symptoms: Subcutaneous tenderness, redness and swelling, and hot to the touch.
- Pathogenesis: Coagulase and exfoliatins.
Impetigo Contagiosa
- Clinical Symptoms: Erythematous papules to bullae usually on the cheeks which rupture, producing discharge and then honey-colored crusts.
- Pathogenesis: Coagulase and exfoliatins, skin-exfoliating toxins.
Scalded Skin Syndrome
- Clinical Symptoms: Diffuse epidermal peeling.
- Pathogenesis: Exfoliatins.
Surgical Infections
- Clinical Symptoms: Fever with cellulitis and/or abscesses.
- Pathogenesis: Coagulase, exfoliatins, and TSSTs.
Carbuncle
- Clinical Symptoms: Multiple skin abscesses with interconnected cavities horizontally and connected to the skin surface by tracks draining pus. Usually occur in diabetics at the napes or in immunocompromised individuals with infected wounds.
- Pathogenesis: Coagulase, exfoliatins, and TSSTs.
MRSA (Methicillin-Resistant S. aureus)
- Clinical Symptoms: Important cause of serious nosocomial and community-acquired infections.
- Pathogenesis: Resistance to methicillin and nafcillin due to altered penicillin-binding protein.
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Description
Test your knowledge on Staphylococcus aureus, including its reservoirs, transmission, infections, and pathogenesis. This quiz covers the key concepts related to this bacterium and the diseases it can cause, such as gastroenteritis. Ideal for students in microbiology or infectious diseases.
