Methicillin-Resistant Staphylococcus aureus (MRSA) Infection in Orthopaedics
DNB Orthopaedics • June 2014 • Paper I • 10 Marks
Introduction
Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of hospital- and community-acquired infection and is particularly relevant in orthopaedics because of its ability to cause osteomyelitis, septic arthritis, surgical-site infection and implant-associated infection.
Orthopaedic MRSA infection is difficult to eradicate because of antimicrobial resistance, poor penetration of antibiotics into necrotic bone, and the ability of the organism to form biofilm on implants and devitalised tissue.
Core principle
Successful treatment requires three components: early diagnosis + adequate surgical source control + culture-directed antimicrobial therapy.
Definition and Basis of Resistance
MRSA is a strain of Staphylococcus aureus that is resistant to methicillin and most conventional β-lactam antibiotics because of acquisition of the mecA gene, or less commonly related mec genes, resulting in production of an altered penicillin-binding protein, PBP2a.
PBP2a has a low affinity for β-lactam antibiotics, allowing continued bacterial cell-wall synthesis despite exposure to drugs such as penicillins and many cephalosporins.
Epidemiological Classification
| Type | Typical Setting | Clinical Features |
|---|---|---|
| Healthcare-associated MRSA | Hospitalisation, surgery, nursing facilities, indwelling devices | Surgical-site infection, implant infection, bacteraemia, osteomyelitis |
| Community-associated MRSA | Patients without traditional healthcare exposure |