Resistance Of Stenotrophomonas Maltophilia To Fluoroquinolones:prevalence And Genes In Ningxia

Objective The purpose of this study was to investigate the clinical distribution and genotyping of Stenotrophomonas maltophilia, the resistance to antimicrobial agents, and the genes of drug resistance.Methods S. maltophilia isolates were collected from clinical specimens in a tertiary hospital, northwestern China during the period between 2010 and 2012, and were identified to species level with a fully automated microbiological system. Antimicrobial susceptibility testing was performed for S. maltophilia with the Kirby-Bauer disc diffusion method. The minimal inhibitory concentrations(MICs) of norfloxacin, ofloxacin, chloramphenicol, minocycline, ceftazidime, levofloxacin and ciprofloxacin on S. maltophilia were assessed using agar dilution method, and the changes in the MIC of norfloxacin, ciprofloxacin and ofloxacin were observed after the addition of reserpine, an efflux pump inhibitor. Fluoroquinolone resistance genes was detected in S. maltophilia using a polymerase chain reaction(PCR) assay, and the expression of efflux pump sme D and sme F genes was determined using a real-time fluorescent quantitative(q RT)-PCR assay. Pulsed-field gel electrophoresis(PFGE) was employed to genotype S. maltophilia isolates identified.Results A total of 426 S. maltophilia strains were isolated from the tertiary hospital from 2010 to 2012, consisting of 10.1% of total non-fermentative bacteria. The prevalence of norfloxacin, ciprofloxacin and ofloxacin resistance was 32.4%, 21.9% and 13.2% in the 114 S. maltophilia isolates, respectively. Following reserpine treatment, 19 S. maltophilia isolates positive for efflux pump were identified, and high expression of sme D and sme F genes was detected in 2 resistant isolates. gyr A, par C, sme D, sme E and sme F genes were detected in all 114 S. maltophilia isolates, while smqnr gene was found in 25.4% of total isolates. Glu-Lys mutation(GAA-AAA) was detected at the 151 th amino acid of the gyr A gene, while Gly-Arg mutation(GGC-CGC) was found at the 37 th amino acid of the par C gene. However, no significant difference was observed in the prevalence of gyr A or par C mutation between fluoroquinolone-resistant and-susceptible isolates(P > 0.05). The smqnr gene showed 92% to 99% heterogenicity among the 14 S. maltophilia clinical isolates. PFGE of 29 smqnr gene-positive S. maltophilia clinical isolates rendering scattered distribution.Conclusions 1.The majority of S. maltophilia strains were isolated from the respiratory tract specimens collected from the ICU, department of Respiratory Medicine and Department of Neurosurgery, With phlegm, throat swab, catheters and waste in the highest detection rate.2. S. maltophilia contains a chromosomally encoded qnr gene(Smqnr) which confers low-level resistance to fluoroquinolones and together with the efflux pump resistant genes.3. We demonstrated that in our hospital S. maltophilia did not appear the same clone strains outbreaks by PFGE technique, rendering scattered distribution.