Staphylococcus aureus has been known to be a major pathogen causing a wide spectrum of clinical manifestations, such as wound infections, pneumonia, septicemia, and endocarditis, with beta-lactam antibiotics being the drugs of choice for therapy. Since the introduction of methicillin into clinical use in 1961, the occurrence of methicillin-resistant S. aureus (MRSA) has steadily increased and nosocomial infections caused by such isolates have become a serious problem worldwide. The differentiation of MRSA strains from other strains of S. aureus has important implications for the treatment and management of patients with S. aureus infections, and glycopeptides are the drugs of choice for infections caused by MRSA strains. Furthermore, evidence of MRSA requires extensive hygienic precautions to limit the spread of such strains. Detection of the mecA gene by PCR has been described as a rapid method for the identification of MRSA. The sa442 gene, which is unique to S. aureus, is used as an identification tool in cases where the phenotype is unclear.
DNA is extracted from colonies or liquid media. The mecA and sa442 genes are PCR-amplified on the LightCycler using gene-specific primers, with subsequent SYBR green melting curve analyses. The presence of a PCR product, and characteristic melting curves identical to that of MRSA confirm the presence of the mecA and sa442 genes.
The mecA and sa442 tests can be ordered separately.