Introduction

Staphylococcus aureus is a common skin and nasopharynx commensal, and is carried in the nose of 30% of people.  Staphylococcus aureus is one of the commonest causes of both endemic and epidemic nosocomial infections, with substantial morbidity and mortality.  The emergence of methicillin-resistant Staphylococcus aureus (MRSA) was reported in Europe in the early 1960s and is still a major concern today.  In 2001, 42% of the 13,084 Staphylococcus aureus bacteraemias reported in England and Wales were methicillin-resistant as compared to 2% in 1992 (PHLS).  MRSA is easily spread by direct contact, most often via the hands of transiently colonised healthcare workers.

Emergence of MRSA

More than 80% of Staphylococcus aureus strains produce penicillinases and therefore penicillinase-stable beta-lactams, such as methicillin, cloxacillin and flucloxacillin, have been the mainstay of treatment of Staphylococcus aureus infections for over 35 years.  Methicillin-resistant Staphylococcus aureus (MRSA) emerged shortly after the introduction of these agents to clinical practice.  Methicillin resistance developed from production of a penicillin-binding protein (PBP2a) which has a low affinity to beta-lactams, allowing cell wall synthesis to continue in their presence.  This protein therefore confers resistance to the beta-lactamase-resistant penicillins and cephalosporins. 

Strains of MRSA may be ‘epidemic’ (EMRSA) or multi-drug resistant, with variable resistance to clindamycin, erythromycin, tetracycline, trimethoprim/sulfamethoxazole, fluoroquinolones, aminoglycosides and rifampicin.

Recent reports have also highlighted the emergence of Staphylococcus aureus with intermediate-level resistance to vancomycin (MIC 8 mg/l), with additional implications for the management of MRSA infection.

Factors affecting susceptibility to MRSA infection

• Vulnerable patients.
• Invasive indwelling devices.
• Patients with wounds.
• Extended hospitalisation.
• Prior or prolonged antibiotic therapy.
• Chronic underlying disease.

Management of MRSA infection

If MRSA is suspected seek advice from your local microbiologist and consult local guidelines.

Guidelines for the management and prevention of MRSA were reported by a Combined Working Party of the British Society for Antimicrobial Chemotherapy, the Hospital Infection Society and the Infection Control Nurses Association.

Principles of treatment

Indwelling catheters should be removed and any abscesses drained.

Monotherapy should be avoided to prevent emergence of additional drug resistance in MRSA isolates.

Severe or life threatening infection

Treatment options include:

• A glycopeptide such as vancomycin or teicoplanin, or an oxazolidinone such as linezolid, in combination with rifampicin.

Moderate infection

Treatment options include:

• Combinations of a number of antibiotics such as fusidic acid, rifampicin, trimethoprim, clarithromycin and erythromycin depending on the susceptibility and resistance patterns of the organisms.