The new genetic environment of cfr on plasmid pBS-02 in a Bacillus strain

Sir, The gene cfr, encoding a 23S rRNA methyltransferase, confers resistance to five chemically unrelated antimicrobial classes, including phenicols, lincosamides, oxazolidinones, pleuromutilins and streptogramin A (PhLOPSA), and has been observed mainly in staphylococcal isolates over the past decade.1–3 Our previous study reported a cfr-carrying plasmid, pBS-01, in a novel strain (BS-01) of a Bacillus species isolated from a pig farm in China.4 In our routine surveillance study on antimicrobial resistance in farm animals in 2010, another florfenicol and chloramphenicol-resistant Bacillus species strain (named BS-02) from swine faeces was identified. Gram staining, sequence analysis of the 16S rRNA and API 50CH testing associated with the API 20E system (bioMérieux, France) showed that BS-02 had an identical profile to that of strain BS-01, which suggested that BS-02 also belongs to a novel Bacillus species. Despite their identical profiles, more than six PFGE band differences were observed between BS-01 and BS-02 (data not shown), indicating that they belong to different clonal types of the same species.