A-047. Detection of cfr rRNA Methyltransferases among Staphylococcus aureus (SA) and Coagulase-Negative Staphylococci (CoNS) Recovered from Human Infections
Background: Cfr, a chloramphenicol resistance (R) gene in S. sciuri, also mediates R to lincosamides, streptogramin A, oxazolidinones and pleuromutilins, and has subsequently been found in S. simulans and SA, all of animal origin. Only one report of a cfr-positive human source SA (Columbia) has been described. This methyltransferase produces R by methylation of adenosine at position 2503 of the 23S rRNA. Here we describe identification of the cfr gene in SA and CoNS recovered from human infections. Methods: Staphylococci recovered as part of international surveillance and research programs that demonstrated R to chloramphenicol, linezolid, clindamycin and quinupristin/dalfopristin when tested by the CLSI broth microdilution assay were further evaluated by PCR and amplicon sequencing for the linezolid-R G2576T mutation in the 23S rDNA and for the cfr gene (Kehrenberg et al. Antimicrobial Agents Chemother 2006;50:1156). Plasmid analysis followed by cfr amplification/sequencing was also performed. Results: Four isolates meeting criteria were identified in 2006-2007, including two each SA (USA and Belgium) and CoNS (USA and Spain). All displayed a multidrug-resistant phenotype (see Methods) including R to oxacillin and ciprofloxacin. Two were R to erythromycin (Cfr-mediated methylation does not affect macrolide S), and concurrent presence of ermA was documented; all isolates were susceptible to vancomycin. While the G2576T mutation was not detected, all four were positive for cfr, confirmed by sequencing. Preliminary evaluation revealed presence of the cfr gene on plasmids in two strains. The genetic context of cfr differs from prior reports in some strains. Conclusion: This is the first report of cfr-mediated linezolid-R among SA and CoNS in USA and European human isolates. The potential mobility of this gene via plasmidic spread, combined with the tendency towards clonal dissemination among Staphylococcus spp., is a serious threat to potent Gram-positive-active agents, including oxazolidinones. Active surveillance along with effective infection control should be utilized in minimizing spread of this worrisome R mechanism.