Methicillin-Resistant Staphylococcus Aureus (MRSA) is a gram-positive bacteria that is resistant to the penicillin family of antibiotics. Staphylococcus aureus is a common bacteria that causes skin and soft-tissue infections. While previously easily treated with penicillins, overuse of antibiotics has placed selective pressure on many bacteria to develop antibiotic resistance.
MRSA was first a problem in healthcare facilities, such as nursing homes and hospitals, but has become widespread throughout the community. It is usually seen as a skin or soft tissue infection, but can also cause urinary tract infections, pulmonary infections, and sepsis. As a skin infection, it presents as a dark red swollen area, painful and warm to the touch, and will usually develop purulent drainage. It is often mistaken for a spider or insect bite. Risks for infection include breaks in the skin, poor nutritional status, immunocompromised, poor hygiene, and crowded living conditions. Infections beyond the skin can quickly become serious and life-threatening.
MRSA can be carried on the skin and in the nasal cavity without obvious infection. It is estimated that 5% of people are carriers of MRSA at any one time. MRSA is spread by direct contact with the infected area or drainage from the area, so strict hygiene measures are vital to the prevention and control of infection.
The resistance to penicillins (beta-lactam family of antibiotics) is due to a mutation in the mecA gene. This mutation causes S. aureus to bind poorly to penicillins, making it resistant to their effects. Identification of MRSA can be done through culture and direct observation for growth in the presence of a beta-lactam antibiotic, usually cefoxitin. Another method is PCR (Polymerase Chain Reaction) testing for S. aureus and the mecA gene. PCR testing is being used more as it has become more widely available and is often used in conjunction with culture and susceptibility testing. This provides an accurate clinical picture and guides the best treatment for the patient.