Stenotrophomonas maltophilia is an important pathogen in healthcare-associated infections. S.maltophilia may contain Sm. qnr, a quinolone resistance gene encoding the pentapeptide repeat protein, which confers low-level quinolone resistance upon expression in a heterologous host. We investigated the prevalence of Sm. qnr and plasmid-mediated quinolone resistance (PMQR) determinants in S.maltophilia isolates from Japan. A total of 181 consecutive and nonduplicate clinical isolates of S.maltophilia were collected from four areas of Japan. The antimicrobial susceptibility profiles for these strains were determined. PCR was conducted for Sm. qnr and PMQR genes, including qnrA, qnrB, qnrC, qnrS,aac(6')-Ib and qepA. PCR products for Sm. qnr and aac(6')-Ib were sequenced. For the S.maltophilia isolates containing Sm. qnr, pulsed-field gel electrophoresis (PFGE) was performed using XbaI. Resistance rates to ceftazidime, levofloxacin, trimethoprim-sulfamethoxazole, chloramphenicol and minocycline were 67.4%, 6.1%, 17.7%, 8.8% and 0%, respectively. The minimum inhibitory concentration required to inhibit the growth of 50% and 90% of organisms were 0.5 and 2mg/L for moxifloxacin but 1 and 4mg/L for levofloxacin, respectively. Sm. qnr was detected in 104 of the 181 S.maltophilia isolates (57.5%), and the most frequent was Sm. qnr6, followed by Sm. qnr8 and Sm. qnr11. Eleven novel variants from Sm. qnr48 to Sm. qnr58 were detected. The 24 Sm. qnr-containing S.maltophilia isolates were typed by PFGE and divided into 21 unique types. Nine S.maltophilia isolates (5.0%) carried aac(6')-Ib-cr. No qnr or qepA genes were detected. This study describes a high prevalence of Sm. qnr and novel variants of Sm. qnr among S.maltophilia from Japan. Continuous antimicrobial surveillance and further molecular epidemiological studies on quinolone resistance in S.maltophilia are needed.
- Antimicrobial susceptibility
- Plasmid-mediated quinolone resistance (PMQR)
- Stenotrophomonas maltophilia