We investigated the genetic basis of glycopeptide resistance in laboratory-derived strains of S. haemolyticus with emphasis on differences between vancomycin and teicoplanin. The genomes of two stable teicoplanin-resistant laboratory mutants selected on vancomycin or teicoplanin were sequenced and compared to parental S. haemolyticus strain W2/124. Only the two non-synonymous mutations, VraS Q289K and WalK V550L were identified. No other mutations or genome rearrangements were detected. Increased cell wall thickness, resistance to lysostaphin-induced lysis and adaptation of cell growth rates specifically to teicoplanin were phenotypes observed in a sequenced strain with the VraS Q289K mutation. Neither of the VraS Q289K and WalK V550L mutations was present in the genomes of 121S. haemolyticus clinical isolates. However, all but two of the teicoplanin resistant strains carried non-synonymous SNPs in vraSRTU and walKR-YycHIJ operons pointing to their importance for the glycopeptide resistance.

Department of Chemistry Norstruct UiT The Arctic University of Norway Sykhusvegen 23 Tromsø 9019 Norway

Department of Pediatrics University Hospital of North Norway Sykehusvegen 38 Tromsø 9019 Norway; Department of Clinical Medicine UiT The Arctic University of Norway Tromsø 9037 Norway

Institute of Microbiology v v i The Czech Academy of Sciences Průmyslová 595 Vestec 252 50 Czech Republic

Institute of Microbiology v v i The Czech Academy of Sciences Vídeňská 1083 Prague 142 20 Czech Republic

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