Staphylococci (Catalase positive)

Question 1

S. aureus

Answer 1

Gram (+), Coagulase +, Protein A (virulence factor - binds Fc portion of IgG inhibiting complement fixation and phagocytosis). Teichoic acid toxin (helps staph adhere to mucosal cells, mediates septic shock syndrome, like lipid A in gram negative organisms).

“Inflammatory: Skin infections. Organ absecesses, pneumonia.
Toxin-mediated: TSST-1 (superantigen binds to MHC-II and T-cell receptor resulting in polyclonal T-cell activation. presents as fever, vomiting, rash, desquamation, shock, organ failure), scalded skin (exfoliative toxin)(Ritter’s disease in newborns), rapid-onset food poisoning (enterotoxin). Staph. aureus food poisoning = pre-formed toxin.
MRSA: nosocomial, resistant to beta-lactam antibiotics
Acute bacterial endocarditis, osteomyelitis. Exotoxin (kills leukocytes)”

Question 2

S. epidermidis

Answer 2

Normal skin flora. Biofilm, novobiocin sensitive.

Nosocomial, IV line infections, prosthetic devices (heart valves), contaminates blood cultures