Staphylococcal Cassette Chromosome mec (SCCmec) in coagulase negative staphylococci

Coagulase-negative staphylococci (CoNS) are among the main causative agents of bacteremia. Staphylococcus epidermidis and Staphylococcus haemolyticus are the CoNS species most frequently isolated. These species are often associated with infections in immunocompromised patients who have a medical device implant. Methicillin resistance was first described in Staphylococcus aureus; it has also been reported in CoNS species. Methicillin resistance is conferred by expression of the mecA gene, contained within the staphylococcal cassette chromosome (SCCmec). mecA gene codes for the PBP2a protein which shows poor binding to beta-lactam antibiotics, so methicillin-resistant strains are resistant to beta-lactams. The presence of SCCmec in CoNS species complicates infections caused by these organisms, since it confers resistance to a variety of antibiotics, making treatment difficult. This review analyzes the clinical relevance of SCCmec as well as the diversity and structure of elements present in CoNS species.