Identification and Characterization of the Multidrug Resistance Gene cfr in Panton-Valentine Leukocidin-Positive ST8-Methicillin-Resistant Staphylococcus aureus-IVa (USA300) Isolate

The staphylococcal cfr gene mediates resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins and streptogramin A, a phenotype that has been termed PhLOPSA. The cfr gene has mainly been associated with coagulase-negative staphylococcal isolates from animals and only a few cfr-positive methicillin-resistant Staphylococcus aureus (MRSA) isolates have been described so far. This study reports the first description of a cfr-positive MRSA isolate (M05/0060) belonging to the pandemic Panton-Valentine Leukocidin (PVL)-positive ST8-MRSA-IVa/USA300 clone. The cfr gene was detected in M05/0060 using a DNA microarray which was used to screen PVL-positive MRSA isolates for the presence of virulence genes, typing markers and antimicrobial resistance genes. Antimicrobial susceptibility testing revealed that M05/0060 exhibited the cfr-associated resistance phenotype. Molecular analysis identified the presence of cfr and a second phenicol resistance gene fexA on a novel 45-kb conjugative plasmid, which was, designated pSCFS7. Within pSCFS7, a DNA segment consisting of cfr, a truncated copy of insertion sequence IS21-558 and a region with homology to the DNA invertase gene bin3 of transposon Tn552 from Bacillus mycoides, was integrated into the transposase gene tnpB of the fexA-encoding transposon Tn558. The emergence of a multidrug-resistant cfr-positive variant of ST8-MRSA-IVa/USA300 is alarming and requires ongoing surveillance. Moreover, the identification of a novel conjugative plasmid carrying the cfr gene indicates the ability of cfr to spread to other MRSA strains