Staphylococcus aureus

1. Gram-positive cocci, in clusters.
2. Catalase +, Coagulase + (differentiates from other staph).  
3. Golden-yellow, beta-hemolytic colonies.  
4. Grows on mannitol salt agar (ferments mannitol).  
5. Virulence: Protein A, coagulase, hemolysins, enzymes.  
6. Toxins:  
   - Enterotoxin – food poisoning  
   - TSST-1 – toxic shock  
   - Exfoliative – scalded skin  
7. Diseases:  
   - Skin (boils, impetigo)  
   - Systemic (pneumonia, osteomyelitis, endocarditis)  
   - Toxin-mediated (TSS, food poisoning)  
8. MRSA: mecA gene → PBP2a → resistant to beta-lactams.  
9. Treatment
   - MSSA: cloxacillin  
   - MRSA: vancomycin/linezolid  
10. Normal flora of nose, skin, causes hospital infections.

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