MOLECULAR TYPING OF THE METHICILLIN RESISTANCE DETERMINANT (MEC) OF CLINICAL STRAINS OF STAPHYLOCOCCUS BASED ON MEC HYPERVARIABLE REGION LENGTH POLYMORPHISMS

We used a method for molecular typing the methicillin resistance deter minant (mec) based on the size of the mec-associated hypervariable reg ion amplified by the polymerase chain reaction (PCR) to examine 61 met hicillin-resistant Staphylococcus aureus (MRSA), 15 methicillin-resist ant (Mc') 6 epidermidis, and 11 Mc' S. haemolyticus clinical isolates. In the 61 MRSA isolates, five sizes of PCR products were observed. Th e MRSA isolates were grouped into five hypervariable region (HVR) geno types on the basis of the size of the PCR product. Three different siz es were detected among 15 isolates of Mc' S. epidermidis and two sizes among 11 isolates of Mc' S. haemolyticus. The PCR products amplified from 14 of 15 Mc' S. epidermidis isolates were the same as products am plified from MRSA isolates, which was confirmed by the PCR-SSCP (singl e-strand conformation polymorphism) method. In methicillin-susceptible isolates, the target gene was not amplified. This method is thought t o be useful in epidemiologic investigations of nosocomial infections c aused by MRSA. This is the first typing method capable of comparing th e mec determinants of MRSA isolates and Mc' coagulase-negative staphyl ococcal isolates to establish the origin of the mec determinant.