A combined molecular approach to screen for mec gene variants from methicillin-resistant Staphylococcus aureus

Previous reports have suggested a common origin for all methicillin resistance (mec) genes from methicillin-resistant Staphylococcus aureus (MRSA) isolates examined so far. The purpose of this study was to explore several molecular methods for screening MRSA isolates from different sources and, in some cases, with varying phenotypes. Eighty MRSA isolates from three teaching hospitals in the University of Louisville Medical Center were compared with MRSAs from a hospital in southern California and with methicillin-sensitive S. aureus isolates. The methods were used to detect the presence of mec gene and to screen for any polymorphisms in these genes for the respective strains. The mec gene for each isolate was amplified via the polymerase chain reaction, and each polymerase chain reaction product was compared to the others by restriction enzyme digestion, denaturing-gradient gel electrophoresis, and mutation detection enhancement. By these criteria, the mec genes from the 80 MRSA strains in this study seemed to be identical. Such a finding was not unexpected and supported the existing hypothesis of a common ancestor for all mec genes isolated in MRSA isolates. However, the combination of methods used in this study may facilitate screening of MRSA strains in population studies as mec gene variants begin to emerge.