Staphylococcus aureus (which is occasionally given the nickname golden staph) is a bacterium, frequently living on the skin or in the nose of a healthy person, that can cause illnesses ranging from minor skin infections (such as pimples, boils, and cellulitis) and abscesses, to life-threatening diseases such as pneumonia, meningitis, endocarditis and septicemia. Each year some 500,000 patients in American hospitals contract a staphylococcal infection.
Microbiology
Staphylococcus aureus appears as a Gram-positive coccus, in grape-like clusters when viewed through a microscope and as large, round golden-yellow colonies, with beta-haemolysis when grown out on agar plates. Staphylococcus aureus is differentiated from most other staphylococci by the coagulase test. Staphylococcus aureus is coagulase-positive, while all other Staphylococci are coagulase-negative.
Antibiotic sensitivity
S. aureus has become resistant to many commonly used antibiotics. Up to 20% of all Staphylococcus isolates is resistant to penicillin, which has led to the introduction of flucloxacillin as first-line antistaphylococcal antibiotic.
An increasing problem since the 1950s has been resistance of S. aureus to flucloxacillin, oxacillin and similar β-lactamase resistant antibiotics. As methicillin is used in laboratories to assess for this type of resistance, the term Methicillin-resistant Staphylococcus aureus (MRSA) is in use to denote these strains. MRSA is generally sensitive to the glycopeptide antibiotics vancomycin and teicoplanin.
In 1997, physicians were alarmed to encounter staph strains that resist even vancomycin, to which it had previously always been sensitive. Due to this resistance, S. aureus is sometimes referred to as a superbug although it is in fact no more infectious than before it acquired this antibiotic resistance.
Staphylococcal resistance to penicillins and cephalosporins is expressed as beta-lactamase production: enzymes which break down the beta-lactam ring of the penicillin molecule. Other resistance-conferring mutations include altered penicillin-binding proteins to which penicillins bind poorly.
Role in disease
The Staphylococcus lives as a commensal on the skin and in the nose, but can infect other tissues when normal barriers have broken down (e.g. skin or mucosal lining). This leads to furuncles (boils) and carbuncles (a collection of furuncles).
Staph infections can be spread through contact with pus from an infected wound, skin to skin contact with an infected person, and contact with objects such as towels, sheets, clothing, or athletic equipment used by an infected person.
Deep Staphylococcus infections can be very severe. Prosthetic joints are particularly at risk, and staphylococcal endocarditis (infection of the heart valves) may be rapidly fatal.
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Last updated: 10-24-2005 15:21:20
