Staphylococcus Aureus

• Virulent, nonmotile, nonsporeforming, facultative anaerobe,
  
• Gm +ve cocci in grapes/clusters
• Catalase +ve
• Coagulase +ve
• Ubiquitous in environment; normal flora of skin/nose
• Spread through lesions, fomites

• Enterotoxin- vomiting, diarrhea, heat resistant, (actually released in gut)
• TSST-1 – tampon use, wounds, superantigen
• Exfoliatin- scalded skin

TISSUE SPREAD:

• Alpha toxin(lechthinase)- skin necrosis;hemolysis
• Hyaluronidase- degrades proteoglycans
• Fibrinolysin- lysis fibrin clots

IMMUNE EVASION:

• Protein A- binds IgG-Fc, blocks opsonization and complement fixation
• Coagulase- activates prothrombin
• Hemolysin- destroys RBCs, PMNs, M0s, platelets
• Leukocidin- destroys WBCs

• Skin infections: impetigo, cellulitis, erysipelas, abcess, furuncle, carbuncle
  

• Bacteremia/sepsis: hematogenous spread
  

• Acute endocarditis: DESTRUCTIVE (compare to S.viridans and S.faecalis)

• Pneumonia –damaging process, cavitations, empyema, effusions

• Osteomyelitis/septic arthritis- hematogenous and traumatic spread

• Food poisoning – 1-8 hr onset, vomiting, preformed toxin

• Toxic shock syndrome- fever, vomiting, diarrhea, diffuse erythematous rash

• Gm + cocci in grapes,
• Catalase differentiates from Strep.
• S.aureus: Beta hemolysis, coagulase, Yellow (Au) pigment
  

1. (coagulase causes coagulation!)
   

Coagulase neg:
S. epidermidis: novobiocin sensitive

1. “sensitive skin”

S. saprophyticus: Novobiocin resistant

Treatment

• Beta lactamase production is common! Use methicillin, nafcillin, dicloxacillin
• MRSA: (Methicillin resistant S. aureus) : vancomycin
  

Category: Microbiology Notes