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author:("mccall, Carlo")
1.  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 ≤ 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 ≥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 ≥1 mg/L. SCCmec IV isolates were more likely to have vancomycin MICs ≤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.
doi:10.1093/jac/dkp047
PMCID: PMC2667134  PMID: 19261624
MRSA; SCCmec types; clonal types; Staphylococcus spp.
2.  Microbiological and Genotypic Analysis of Methicillin-Resistant Staphylococcus aureus Bacteremia▿  
In a recent landmark trial of bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) isolates, vancomycin MICs were ≥1 μg/ml for only 16% of the isolates, and accessory gene regulator (agr) function as measured by delta-hemolysin activity was absent or reduced in only 28.1% of the isolates. This clinical study did not capture a population of MRSA isolates predictive of vancomycin treatment failure.
doi:10.1128/AAC.00357-08
PMCID: PMC2533503  PMID: 18606839

Results 1-2 (2)