Characterization of a genomic island in Stenotrophomonas maltophilia that carries a novel floR gene variant

Objectives To characterize the chromosomally encoded novel floR gene variant floRv from Stenotrophomonas maltophilia of porcine origin and elucidate the gene order and content of the floRv-flanking regions in an MDR genomic island (GI). Methods Whole genome sequencing was used to identify the unknown florfenicol resistance gene in S. maltophilia strain GZP-Sm1. The candidate gene was cloned into pMD19-T and Escherichia coli transformants carrying this vector were tested for phenicol MICs. Flanking sequences of the florfenicol resistance gene were identified by a de novo assembly and a primer walking strategy. Results GZP-Sm1 carried a floR gene variant, designated floRv. E. coli clones carrying this gene were resistant to chloramphenicol and florfenicol. The deduced 404 amino acid FloRv protein showed 84.1%–91.8% amino acid identity to various FloR proteins. The gene floRv was located in an MDR region within a 40 226 bp GI region. Six resistance genes, including floRv (phenicol resistance), tetR-tetA(A) (tetracycline resistance), strA/strB (streptomycin resistance), sul1 (sulphonamide resistance) and aadA2 (streptomycin/spectinomycin resistance), were located in this MDR region. PCR analysis revealed that the GI was not stable and could be excised from the chromosome as a circular intermediate. Conclusions The floRv gene was identified in a porcine S. maltophilia isolate. Six resistance genes including floRv were located in a novel GI. As an opportunistic pathogen in animals and humans, S. maltophilia might act as a resistance gene reservoir in farm environments. Its contribution to the spread of resistance genes to other pathogens should be monitored.