Genotypic identification of methicillin-resistant coagulase-negative staphylococci by polymerase chain reaction

A rapid method for the detection of methicillin resistance in staphylococci was developed. The method was based on the polymerase chain reaction (PCR) and primers that targeted the internal region of the coding frame of the mec gene. The amplification reaction was carried out with crude cell lysates as a source of target DNA and provided data in less than 5 h. Seventy-four isolates of coagulase-negative staphylococci were tested by PCR, DNA hybridization with a probe derived from the mec gene, and an agar dilution susceptibility assay. PCR results showed a 100% correlation with the susceptibility assay carried out with high inocula (10(8) CFU) and incubation at 32 degrees C for 48 h. PCR was more sensitive and specific than DNA hybridization in detecting methicillin resistance in coagulase-negative staphylococci. The former technique identified the mec gene in all the strains which were phenotypically resistant but which did not hybridize with the probe. Identification of methicillin-resistant strains by PCR offers a very specific, sensitive, and rapid alternative to traditional susceptibility tests and DNA hybridization as a guide for the treatment of infections caused by staphylococci.