[Molecular typing of the methicillin resistance determinant (mec) of clinical strains of Staphylococcus based on mec...

We used a method for molecular typing of the methicillin resistance determinant (mec) based on the size of the mec-associated hypervariable region amplified by the polymerase chain reaction (PCR) to examine 106 methicillin-resistant Staphylococcus aureus (MRSA), 9 methicillin-resistant (Mcr) S. epidermidis and 5 Mcr S. haemolyticus clinical isolates. In the 106 MRSA isolates, 5 sizes of PCR products were observed. The MRSA isolates were grouped into five hypervariable region (HVR) genotypes on the basis of the size of the PCR product. The PCR products amplified from 8 of 9 Mcr S. epidermidis isolates were the same as products amplified from MRSA isolates, which was confirmed by the PCR-SSCP (single-strand conformation polymorphism) method. In 32 methicillin-susceptible isolates, the target gene was not amplified. This method is thought to be useful in epidemiological investigations of nosocomial infections caused by MRSA. This is the first typing method capable of comparing the mec determinants of MRSA isolates and Mcr CNS isolates to establish the origin of the mec determinant.