Identification and Characterization of the Multidrug Resistance Gene cfr in a Panton-Valentine Leukocidin-Positive Sequence Type 8 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 PhLOPS A . 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 sequence type 8 MRSA IVa/USA300 (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 IS 21 - 558 , and a region with homology to the DNA invertase gene bin3 of transposon Tn 552 from Bacillus mycoides was integrated into the transposase gene tnpB of the fexA -carrying transposon Tn 558 . 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.