Abstract
Objective: The purpose of this study was to investigate the clinical distribution and genotyping of Stenotrophomonas maltophilia, its resistance to antimicrobial agents, and the possible mechanisms of this drug resistance. Methods: S. maltophilia isolates were collected from clinical specimens in a university hospital in Northwestern China during the period between 2010 and 2012, and were identified to the 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 against S. maltophilia were assessed using the agar dilution method, and changes in the MIC of norfloxacin, ciprofloxacin and ofloxacin were observed after the addition of reserpine, an efflux pump inhibitor. Fluoroquinolone resistance genes were detected in S. maltophilia using a polymerase chain reaction (PCR) assay, and the expression of efflux pump smeD and smeF genes was determined using a quantitative fluorescent (QF)-PCR assay. Pulsed-field gel electrophoresis (PFGE) was employed to genotype identified S. maltophilia isolates. Results: A total of 426 S. maltophilia strains were isolated from the university 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 collected from 2012, respectively. Following reserpine treatment, 19 S. maltophilia isolates positive for efflux pump were identified, and high expression of smeD and smeF genes was detected in two resistant isolates. gyrA, parC, smeD, smeE and smeF 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 151th amino acid of the gyrA gene, while Gly-Arg mutation (GGC-CGC) was found at the 37th amino acid of the parC gene. However, no significant difference was observed in the prevalence of gyrA or parC 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 revealed 25 PFGE genotypes and 28 subgenotypes. Conclusions: Monitoring the clinical distribution and antimicrobial resistance of S. maltophilia is of great significance for the clinical therapy of bacterial infections. Reserpine is effective to inhibit the active efflux of norfloxacin, ciprofloxacin and ofloxacin on S. maltophilia and reduce MIC of fluoroquinolones against the bacteria. The expression of efflux pump smeD and smeF genes correlates with the resistance of S. maltophilia to fluoroquinolones.
Highlights
Stenotrophomonas maltophilia, an aerobic, non-fermentative bacterium, is predominantly found in immunocompromised individuals and those receiving long-term, large-dose broad-spectrum antimicrobial agents [1,2,3]
Monitoring the clinical distribution and antimicrobial resistance of S. maltophilia is of great significance for the clinical therapy of bacterial infections
We investigated the distribution and antimicrobial resistance of 426 clinical strains of S. maltophilia isolated during the period between 2010 and 2012from a university hospital located in Northwestern China, and explored the possible mechanisms of the observed resistance, so as to provide evidence as a basis for the inappropriate clinical use of antimicrobial agents and the control and prevention of S. maltophilia infections
Summary
Stenotrophomonas maltophilia, an aerobic, non-fermentative bacterium, is predominantly found in immunocompromised individuals and those receiving long-term, large-dose broad-spectrum antimicrobial agents [1,2,3]. This bacterium, which frequently colonizes medical devices, may induce catheter-associated infections, bacteriaemia, urinary infections, and infections at other multiple sites [4,5]. Fluoroquinolones are a class of chemicals that are effective for the treatment of infections caused by S. maltophilia infections [9,10,11], there is an increasing reported prevalence of resistance to fluoroquinolones in. It is reported that the resistance of S. maltophilia to fluoroquinolones may be mainly caused by the mutation at the target sites of DNA gyrase and topoisomerase [15,16,17,18], plasmid or chromosome-mediated mutations of drug resistance genes [19,20] and drug efflux pumps [21,22,23]
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