Detection of the Smqnr quinolone protection gene and its prevalence in clinical isolates of Stenotrophomonas maltophilia in China

The aim of this study was to detect novel variants of the Stenotrophomonas maltophilia Smqnr gene family and analyse the prevalence of Smqnr genes in clinical isolates of S. maltophilia in China. In total, 442 clinical isolates of S. maltophilia were collected from nine hospitals in four provinces in China. Antimicrobial susceptibility testing against six commonly used antibiotics was performed on these isolates. The sequences of the Smqnr genes amplified by PCR were aligned with those of known Smqnr genes in GenBank and an Smqnr database. The resistance rate against co-trimoxazole was highest at 48.6%, followed by resistance rates against ceftazidime, chloramphenicol, ticarcillin/clavulanate and tigecycline at 28.7, 21.3, 19.0 and 16.1%, respectively. The highest susceptibility was shown to levofloxacin, with a resistance rate of just 6.1%. Smqnr genes were detected in 114 isolates, and comprised 11 previously identified genes and 20 new variants, bringing the total number of known Smqnr genes to 47. The 20 novel Smqnr genes were designated Smqnr28-47 and the encoded proteins showed only 1-12 amino acid differences among each other. The most common Smqnr genes in China were Smqnr8 and its variant Smqnr35 with prevalences of 17.5% (20/114) and 13.2% (15/114), respectively. Both the known and the novel Smqnr genes were discovered in both quinolone non-sensitive and sensitive isolates with similar frequency, suggesting that the Smqnr gene makes little contribution to quinolone resistance in this organism.