A STUDY OF GENOME POLYMORPHISM OF METHICI LLIN-RESISTANT STAPHYLOCOCCUS-AUREUS STRAINS

Genome polymorphism of methicillin-resistant Staphylococcus aureus (MR SA) strains isolated from patients with hospital infection in differen t geographic regions of the former USSR was studied. Plasmid analysis and DNA fingerprinting using M13 phage probe and rRNA genes were appli ed. Each technique was shown to be an effective tool for genetic typin g and differentiation of MRSA strains closely related by phenotype. Ho wever, the best results in genetic typing of MRSA were obtained when g enome polymorphism was examined using the universal DNA probe phage M1 3. A complete study of genome polymorphism of MRSA strains closely rel ated by phenotype allowed us to divide them into 13 different genotypi c variants. It was also determined that several different genotypic va riants of MRSA strains can circulate simultaneously in the same hospit al. This fact allowed us to suppose that the appearance, formation, an d spreading of MRSA strains in hospitals can result from two events: ( 1) superinfection of an MRSA strain into a hospital from the outer env ironment, followed by spreading of the strain, and (2) genetic transmi ssion of the met(R) determinant from an MRSA strain of a defined genot ypic variant to a methicillin-sensitive (MSSA) strain of the same or a nother genotypic variant.