Genotypic and phenotypic relationships among methicillin-resistant Staphylococcus aureus from three multicentre bacteraemia studies.
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.
Moise
Pamela A
PA
University of the Pacific, Stockton, CA, USA.
Smyth
Davida S
DS
Robinson
D Ashley
DA
El-Fawal
Nadia
N
McCalla
Carlo
C
Sakoulas
George
G
D016470:Bacteremia / Q000453:epidemiology / Q000382:microbiology*; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000382:microbiology*; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D005838:Genotype; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D011110:Polymorphism, Genetic; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D015534:Trans-Activators / Q000235:genetics
C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D015534:Trans-Activators