Vancomycin Susceptibility within Methicillin-resistant Staphylococcus aureus Lineages

摘要

Methicillin-resistant Staphylococcus aureus (MRSA)with reduced vancomycin susceptibility vancomycin-inter-mediate S. aureus (VISA) has been reported from manycountries. Whether resistance is evolving regularly in differ-ent genetic backgrounds or in a single clone with a geneticpredisposition, as early results suggest, is unclear. Wehave studied 101 MRSA with reduced vancomycin suscep-tibility from nine countries by multilocus sequence typing(MLST), characterization of SCCmec (staphylococcal chro-mosomal cassette mec), and agr (accessory gene regula-tor). We found nine genotypes by MLST, with isolates withinall five major hospital MRSA lineages. Most isolates(88/101) belonged to two of the earliest MRSA clones thathave global prevalence. Our results show that reduced sus-ceptibility to vancomycin has emerged in many successfulepidemic lineages with no clear clonal disposition.Increasing antimicrobial resistance in genetically distinctpandemic clones may lead to MRSA infections that willbecome increasingly difficult to treat