Staphylococcus

Staphylococcus aureus is the most common cause of hospital-acquired infection. It can infect any tissue, but commonly causes wound infection (1.6% of all surgical interventions become infected with S. aureus), pneumonia and bacteremia. The severity of disease varies widely - most infections are relatively minor while others can be fatal. In the community, S.aureus is a frequent cause of skin infections, and is responsible for toxin-mediated diseases such as food poisoning and toxic shock syndrome. 30% of the normal population carry S.aureus as a commensal in their nose.

S.aureus carries the genes for hundreds of known and potential virulence determinants, and it is thought that a combination of these factors play a role in pathogenicity. These factors include proteins that bind the bacteria to host tissue, toxins that destroy tissue and factors that attack or inhibit the immune response.

Treatment. Treatment is by antibiotics such as the b-lactams and, where possible, drainage of the lesion or removal of foreign bodies such as catheters. However, resistance to antibiotics is widespread in hospital strains of S.aureus. About 40% of infections are caused by methicillin-resistant S.aureus (MRSA), and are treated with the antibiotic of last resort, vancomycin. In 2002, the first high-level vancomycin resistant strains of S.aureus were reported in US hospitals.

Vaccines. There is no effective vaccine. Infection rates in hospitals can be lowered, but not eradicated, by improved hygiene methods.