Novel variants of the Smqnr family of quinolone resistance genes in clinical isolates of Stenotrophomonas maltophilia.

BACKGROUND Recent analysis of Stenotrophomonas maltophilia has identified a novel family of resistance genes (Smqnr) encoding pentapeptide repeat proteins, which confer low-level resistance to quinolones. This study describes further novel variants present in clinical isolates of S. maltophilia and investigates their effect on resistance to a number of quinolones in an Escherichia coli host. METHODS PCR for Smqnr alleles was carried out on a selection of S. maltophilia from clinical specimens, and amplicons were cloned and transformed in E. coli TOP10 cells. Transformed colonies carrying the plasmid were tested for susceptibility to a range of quinolones by MIC determination. DNA sequences were determined and translated peptide sequences compared with known SmQnr sequences. RESULTS Thirteen isolates were found to contain Smqnr alleles, of which six corresponded to previously identified Smqnr sequences, while seven were novel variants. Increases in quinolone MICs compared with wild-type E. coli TOP10 were seen for all strains transformed with Smqnr alleles. CONCLUSIONS There is considerable diversity within Smqnr alleles. S. maltophilia may be a significant reservoir for the dissemination of quinolone resistance elements to Enterobacteriaceae.