Staphylococcal infections

[Agnes]

Staphylococci are gram-positive aerobic organisms. Staphylococcus aureus is the most pathogenic; it typically causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis. It commonly leads to abscess formation. Some strains elaborate toxins that cause gastroenteritis, scalded skin syndrome, and toxic shock syndrome. Diagnosis is by Gram stain and culture. Treatment is usually with penicillinase-resistant beta-lactams, but because antibiotic resistance is common, vancomycin or other newer antibiotics may be required. Some strains are partially or totally resistant to all but the newest antibiotics, which include linezolid , tedizolid , quinupristin/dalfopristin , daptomycin , telavancin , dalbavancin , oritavancin , tigecycline , omadacycline, delafloxacin , ceftobiprole (not available in the US), and ceftaroline.
The ability to clot blood by producing coagulase distinguishes the virulent pathogen, Staphylococcus aureus, from the less virulent coagulase-negative staphylococcal species. Coagulase-positive S. aureus is among the most ubiquitous and dangerous human pathogens, for both its virulence and its ability to develop antibiotic resistance.
Coagulase-negative species such as S. epidermidis are increasingly associated with hospital-acquired infections; S. saprophyticus causes urinary infections. S. lugdunensis, a coagulase-negative species, can cause invasive disease with virulence similar to that of S. aureus. Unlike most coagulase-negative staphylococcal species, S. lugdunensis often remains sensitive to penicillinase-resistant beta-lactam antibiotics (ie, methicillin-sensitive).
Pathogenic staphylococci are ubiquitous. They are carried, usually transiently, in the anterior nares of about 30% of healthy adults and on the skin of about 20%; from these locations, staphylococci can cause infection in the host and others. Carriage rates are higher in hospital patients and personnel. S. aureus infections are more prevalent in carriers than in noncarriers and are usually caused by the colonizing strain.