Diseases: abscesses of many organs, endocarditis, gastroenteritis
(food poisoning), toxic shock syndrome, surgical wound infections.
- #1 isolated organism in bacterial tracheitis (membranous croup)
- #1 cause of bacterial pericarditis (strep viridans is a common cause of
bacterial endocarditis, but not bacterial pericarditis)
Characteristics: gram positive cocci in clusters, coagulase positive,
Habitat and Transmission: Habitat is in the human skin and nose.
Transmission is via the hands.
- many enzyme and toxins are made; the two most important are coagulase and
- coagulase is the best correlate of pathogenicity
- enterotoxins cause food poisoning
- Toxic Shock Syndrome Toxin (TSST) is a superantigen that causes toxic
shock syndrome by stimulating many helper T cells to relase large amounts of
lymphokines, especially IL-2
- Protein A is an important virulence factor because it binds to the heavy
chain of IgG and prevents the activation of complement
- predisposing factors are breaks in the skin, foreign bodies such as
sutures, neutrophil levels below 500 microliters, IV drug abuse, tampon use.
- gram stained smear and culture
- yellow or gold colonies on blood agar
- S. aureus is coagulase positive, S. epidermidis is coagulase negative
- Plasmid mediated B-lactamase mediates most resistance
- 85% resistant to penicillin G
- Resistance to nafcillin may be due to changes in binding proteins
- rare vancomycin resistant strains have emerged
- Cefazolin is used to prevent surgical wound infections
- No vaccine is available
- Handwashing reduces spread.
- Penicillin G for sensitive isolates
- B-lactamase-resistant penicillins (ie nafcillin) for resistant isolates
- vancomycin for methicillin-resistant isolates
- Bactrim and clindamycin are effective for community acquired MRSA skin
Levinson and Jawetz. Medical Microbiology and Immunology. 6th edition