This is the first report of the optrA gene in staphylococci and of the coexistence of optrA and cfr on the same plasmid. Dissemination of this plasmid will substantially limit the efficacy of oxazolidinones. Surveillance of optrA in staphylococci of both human and animal origin is urgently warranted.

The multiresistance gene cfr was identified for the first time in streptococci, namely, in porcine Streptococcus suis isolate S10. The cfr gene was detected on the ϳ100-kb plasmid pStrcfr, where it was bracketed by two copies of the novel insertion sequence ISEnfa5, located in the same orientation. The detection of a cfr-and ISEnfa5-containing amplicon by inverse PCR suggests that ISEnfa5 may play a role in the dissemination of cfr.T he cfr gene, encoding a 23S rRNA methyltransferase, confers resistance to five chemically unrelated antimicrobial classes, including phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A (1), as well as decreased susceptibility to the 16-membered macrolides spiramycin and josamycin (2). Since its first identification in a Staphylococcus sciuri isolate of bovine origin (3), this multiresistance gene has been detected in isolates of the genera Staphylococcus, Bacillus, Enterococcus, Macrococcus, Jeotgalicoccus, Proteus, and Escherichia (4). Although florfenicol and lincosamides are used for the control of Streptococcus suis infections, the gene cfr has not yet been reported in streptococci. In a routine surveillance study of antimicrobial resistance of bacteria from farm animals in 2012, a hemolytic, florfenicolresistant (MIC Ն 16 g/ml) streptococcal isolate, S10, was obtained from the nasal swab of an apparently healthy pig at a conventional farm in the Beijing, China, area. Gram staining, colony morphology, and ATB Rapid ID 32 Strep analysis (bioMérieux, Craponne, France) identified isolate S10 as Streptococcus suis. Moreover, 16S rRNA gene sequences, obtained using both universal prokaryotic primers (3) and S. suis-specific primers (5), showed 100% identity to the 16S rRNA gene sequence of S. suis strain NYFC (GenBank accession no. FJ660465.1).S. suis is a global pathogen that causes a wide variety of diseases in swine, such as meningitis, pneumonia, endocarditis, septicemia, and arthritis (6). Of the 35 official serotypes described to date for S. suis, S. suis serotype 2 (SS2) is the most virulent and frequently isolated from diseased animals (7). A PCR assay (5) to detect virulence genes in SS2 isolates, including capsular polysaccharide (cps2J), muramidase-released protein (mrp), extracellular factor (ef), and suilysin (sly), yielded negative results for isolate S10. Rapid serotype-specific PCR screening to detect 15 serotypes of S. suis using previously described primers (8, 9) revealed that S. suis S10 does not belong to any of these serotypes.S. suis S10 was investigated for the presence of the genes cfr, fexA, and fexB, all of which confer florfenicol resistance in Grampositive bacteria, using previously described primers (3). Both cfr and fexA were detected in S. suis S10, and the nucleotide sequence of cfr in isolate S10 showed 100% identity to that of the cfr gene on plasmid pSCFS1 of S. sciuri (GenBank accession no. NC_005076). To the best of our knowledge, this is the first report of either the cfr or the fexA gene in a Streptococcus isolate. Isol...

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Objectives To investigate the presence and transfer of the oxazolidinone/phenicol resistance gene optrA and identify the genetic elements involved in the horizontal transfer of the optrA gene in Streptococcus suis. Methods A total of 237 S. suis isolates were screened for the presence of the optrA gene by PCR. Whole-genome DNA of three optrA-positive strains was completely sequenced using the Illumina MiSeq and Pacbio RSII platforms. MICs were determined by broth microdilution. Transferability of the optrA gene in S. suis was investigated by conjugation. The presence of circular intermediates was examined by inverse PCR. Results The optrA gene was present in 11.8% (28/237) of the S. suis strains. In three strains, the optrA gene was flanked by two copies of IS1216 elements in the same orientation, located either on a prophage or on ICESa2603-family integrative and conjugative elements (ICEs), including one tandem ICE. In one isolate, the optrA-carrying ICE transferred with a frequency of 2.1 × 10−8. After the transfer, the transconjugant displayed elevated MICs of the respective antimicrobial agents. Inverse PCRs revealed that circular intermediates of different sizes were formed in the three optrA-carrying strains, containing one copy of the IS1216E element and the optrA gene alone or in combination with other resistance genes. Conclusions A prophage and two ICESa2603-family ICEs (including one tandem ICE) associated with the optrA gene were identified in S. suis. The association of the optrA gene with the IS1216E elements and its location on either a prophage or ICEs will aid its horizontal transfer.

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