Genetic relatedness of multidrug-resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates from SENTRY antimicrobial resistance surveillance centers worldwide, 1998

We reviewed Staphylococcus aureus bloodstream infection isolates from SENTR Y centers worldwide;during 1998 to evaluate the molecular epidemiology of m ultiply drug-resistant methicillin (oxacillin)-resistant S, aureus (MDR-MRS A), MDR-MRSA was defined as a S, aureus isolate with a MIC for oxacillin at >2 mug/ml and with four or more additional resistances. A total of 325 uni que patient isolates of MDR-MRSA from five continents were analyzed using r ibotyping and pulsed-field gel electrophoresis (PFGE), The frequency of MDR -MRSA among all S, aureus BSI isolates ranged from only 2.2% in Canada to 3 5.6% in the Asia-Pacific region. Forty-eight ribotypes (RT) were distinguis hed, but over 80% of the isolates were contained within the 10 most prevale nt RTs, The most common RT, RT 184.5, which included 30% of all MDR-MRSA, w as found on four of five continents, PFGE provided superior discrimination and identified numerous clusters of possible clonal dissemination of MDR-MR SA within individual medical centers and between institutions that are in g eographic proximity. In four instances,strains with indistinguishable PFGE patterns were found on more than one continent. The predominant PFGE subtyp e in South America (RT 893.5/Ia) was isolated from patients at centers in B razil, Argentina, and Portugal, and closely related subtypes were:isolated- in Chile and Italy. There is great geographic variation in rates of methici llin and multidrug-resistance among S, aureus bloodstream isolates worldwid e, Although many MDR-MRSA strains group geographically, a few closely relat ed epidemic strains have wide regional and even global range.