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Genotypic and phenotypic relationships among methicillin-resistant Staphylococcus aureus from three multicentre bacteraemia studies.
Date: 2009-04-21   Read: 157690

J Antimicrob Chemother. 2009 May;63(5):873-6.

Genotypic and phenotypic relationships among methicillin-resistant Staphylococcus aureus from three multicentre bacteraemia studies.

Moise PA, Smyth DS, Robinson DA, El-Fawal N, McCalla C, Sakoulas G

BACKGROUND: At a time when the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) was changing, we sought to characterize several genotypic markers and glycopeptide susceptibility features of clinical isolates from patients with bacteraemia.

METHODS: One hundred and sixty-eight MRSA bloodstream isolates obtained from three multicentre clinical trials were microbiologically and genotypically characterized.

RESULTS: All isolates were susceptible to vancomycin (MIC < or = 2 mg/L); 38% belonged to accessory gene regulator (agr) group I, 52% belonged to group II and 10% belonged to group III. Typing of the staphylococcal cassette chromosome mec (SCCmec) showed that 67% were type II and 33% were type IV. The agr group II polymorphism was associated with SCCmec II (P < 0.001). Fifty-three percent of SCCmec II and 27% of SCCmec IV isolates had vancomycin MICs > or =1 mg/L (P = 0.001). One hundred percent of agr II strains were predicted to be members of clonal complex 5. SCCmec II was the genetic marker most predictive of vancomycin MICs of > or =1 mg/L. SCCmec IV isolates were more likely to have vancomycin MICs < or =0.5 mg/L.

CONCLUSIONS: Given that SCCmec IV is a marker for a community-based organism for which less prior vancomycin exposure is predicted, we conclude that prior antibiotic exposure in agr group II organisms may account for their increased vancomycin MICs.



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