Study On Quinolone And Sulfonamides Resistant Genes In Clinical Isolates Of Stenoortphomonas Maltophilia

Background:In recent years, the rapid development of medical technology, all sorts of new diagnosis, rescue measures appear ceaselessly, in improved cure rate and rescue success rate but also have certain conditions caused by pathogenic bacteria of hospital infection increases year by year. in order to strengthen anti-infection treatment, a large number of new broad-spectrum antimicrobial drugs continuously published and widely used in clinics, but also accelerate lead to these conditions pathogenic bacteria and multiple resistant pathogens appear, Stenoortphomonas maltophilia is one of them.Stenoortphomonas maltophilia is inherently resistant to most antimicrobials due to a low outer membrane permeability and/or efflux systems, coupled with specific resistance mechanisms, such as the production of two inducible chromosomally encodedβ-lactamases,L1 and L2, and an aminoglycoside acetyltransferase. The few available antibiotics that are naturally active against Stenoortphomonas maltophilia include Ofloxacin Ciprofloxacin and Trimethoprim- Sulfamethoxazole et al.The mechanism of Stenoortphomonas maltophilia acquiring fluoroquinoloes resistance is including three aspects:①the efflux systems coding by smeDEF and smeABC pump out drugs to bacteria②permeability defect, it concerned with the number and quality of permeability protein. The reduction of permeability protein,s quantity or aperture can lead to bacteria resistant.③amino acid mutations in the quinolone-resistance determining regions. The target gene of fluoroquinoloes is topoisomerasesⅡand topoisomeraseaⅣ, which are involved in DNA replication, recombination, and transcription and in the partitioning of the replicated chromosome. Fluoroquinolones combine with the two subunits respectively and DNA to interfere DNA replication, leading to bacteria dead.Stenoortphomonas maltophilia resistant to Trimethoprim- Sulfamethoxazole mainly depends on the resistance genes sul1 and sul2. sul1 and sul2 gene is resistant to dihydrofolate synthetase of sulfa medications, sul1 gene can mediated typeⅠintegration son, and transmit between the different strains. Sul2 is in large plasmid, but few can also be mediated by chromosome, it chain ISCR insert elements common area; the existence of sul1 and sul2 gene are directly related to sulfa-resistance, and the integration son - ISCR structure can be more easily transmit several drug-resistant genes from a plasmid to another plasmid or chromosomes, increasing resistance spread.ObjectiveTo investate the drug resistance of Stenoortphomonas maltophilia strains isolated to fluoroquinoloes and sulfa in our hospital, to examine the genetic mechanisms of resistance by molecular methods and to provide evidence for the clinical therapy of infections.MethodsMicroorganisms were identified by VITEK-40 System and K-B disk diffusion mothod was used for the antibiotics susceptibility test,MICs of Ciprofloxacin﹑Ofloxacin﹑Levofloxacin﹑Gatifloxacin and Trimethoprim- Sulfamethoxazole were determined using agar dilution method which recommend by CLSI. Genes gyrA, gyrB, parC, pare, qnrA,B,S,qepA on plasmid and sul1, sul2 were amplified by polymerase chain reaction(PCR),and some PCR products were sequenced. A total of 128 clinical isolates were analyzed based on WHONET 5.3 software.ResultsA total of 128 strains of Stenoortphomonas maltophilia species were collected from October 2008 to October 2010, The percentage of isolated bacteria in intensive care unit,respiratory department, emergency center and oncology was31.3%,20.3%,16.4%and 10.2% respectively. The resistance rate of Stenoortphomonas maltophilia isolates to Ciprofloxacin,Ofloxacin , Levofloxacin , Gatifloxacin and Trimethoprim- Sulfamethoxazole were 14.8%﹑8.0%﹑ 8.3%﹑ 5.8%﹑ and 7.8% respectively.Polymerase chain reaction(PCR) indicated that all strains of Stenoortphomonas maltophilia have PCR products of gyrA﹑gyrB﹑parC and parE genes , but no products of qnrA﹑ B﹑ S and qepA genes on plasmid, in all Trimethoprim- Sulfamethoxazole- resistance strains there are four strains amplification sul1 genes, but only one strains amplification sul2 genes; DNA sequencing indicated that gyrB and parE gene have no mutations, there are two strains of the point mutations in gyrA genes at codon 57 and the point mutations in parC genes at codon 80 and 44, but no such mutation in sensitive strains.ConclusionThe current status of resistance of Stenoortphomonas maltophilia in Hefei region of China is low, and the resistance to fluoroquinoloes is related to the point mutations within gyrA and parC genes, but isn't related to genes gyrB﹑parE﹑qnrA﹑B﹑S﹑and qepA. the resistance to sulfa is related to sul1 and sul2 genes. Surveillance of bacterial resistance is of great important to rational selection of antibiotics and preventing the abuse of antibiotics and the emergence of new drug-resistant strains.