infectious diseases
Staphylococcal Infections
Introduction
Staphylococci are gram-positive aerobic organisms.Staphylococcus aureusis 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,vancomycinor other newer antibiotics may be required. The ability to clot blood by producing coagulase distinguishes the virulent pathogen,Staphylococcus aureus, from the less virulent coagulase-negative staphylococcal species. Coagulase-positiveS. aureusis among the most ubiquitous and dangerous human pathogens, for both its virulence and its ability to develop antibiotic resistance. Coagulase-negative species such asS. epidermidisare increasingly associated with hospital-acquired infections;S. saprophyticuscauses urinary infections.S. lugdunensis, a coagulase-negative species, can cause invasive disease with virulence similar to that ofS. aureus. Unlike most coagulase-negative staphylococcal species,S. lugdunensisoften remains sensitive to penicillinase-resistant beta-lactam antibiotics (ie, methicillin-sensitive). Acarrier stateis common. 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 hospitalized patients and hospital personnel.S. aureusinfections are more prevalent in carriers than in noncarriers and are usually caused by the colonizing strain. 