| Objective:As Quinolones are commonly used in clinical medicine,bacterial resistance to quinolones in clinical isolates of Escherichia coli has become an increasing problem.Resently the mechanism of plasmid-mediated quinolone resistance have emerged including the genes of qnr,aac(6')-Ib-cr and qepA.The mechanisms provide low-level quinolone resistance,but these genes can horizontal spread and co-select with other resistance elements, especiallyβ-lactamase genes which indicates that amore cautious approach to quinolone use is needed.This study analyzed drug resistance of the clinical isolates in Escherichia coli, then studyed the mechanism of plasmid-mediated quinolone resistance of clinical isolates in Escherichia coli in molecular level and explored the clinical characteristics of patients infected with Escherichia coli which carried plasmid-mediated quinolone resistance determinants for giving a hand on guiding clinical rational use of antimicrobial agents, reduce the bacteria resistant appeared or dissemination.Methods:1,Strains, Susceptibility testing:A total of 143 strains of Escherichia coli were isolated from The Second Hospital of TianJin Medical University from July.2008 to September.2009. Antibiotic susceptibility was tested by micro-dilution broth method.2,Detection of plasmid-mediated quinolone resistance determinants:qmrA,qnrB,qnrS,aac(6')-Ib and qepA were detected by PCR in 75 clinical isolates of Escherichia coli resistant to ciprofloxacin.Positive PCR products of aac(6')-Ib were digested with Fok I to identify aac(6')-Ib-cr.3,Tranfer of qnr in vitro was determined by conjugation experiments with Azide resistant E coli J53 as receipt.The MICs of donors,cotransconjugants and recipient were tested by micro-dilution broth method.4,The existence of ESBLs in plasmid-mediated quinolone resistance determinants-positive strains was detected by PCR.5,Collected and retrospectively analyzed the clinical characteristics of patients infected with plasmid-mediated quinolone resistance determinants-positive Escherichia coli. The clinical characteristics including basic material, clinical material, infection related material and microbial related material.Results:1,Antibiotic susceptibility:Resistant rates of 143 isolates of Escherichia coli against 12 antibiotic were70.63%,58.04%,55.24%,54.54%,52.45%,51.05%,49.65%,48.95%,47.55%,35.66%,12.59%,6.29%respectively.60 strains(41.96%) were multidrug-resistant isolates.2,Distribution of plasmid-mediated quinolone resistance determinants:the qnr gene or aac(6')-Ib-cr gene was identified in 18(24%)strains. The prevalence of qnr or aac(6')-Ib-cr gene is 6.7%and21.3%separatly,the qepA gene were not identified.3,Conjugation experiments were successfully carried out in 5 isolates.4,The ESBLs gene was identified in all of the 18 positive strains, mainly including SHV,CTX-M-1 and CTX-M-9.5,The clinical characteristics of patients infected with positive strains:Positive isolates had high-level resistance against quinolone and cephalosporin.The patients are all elderly and mostly had one or more kinds of a basic diseases.Conclusions:1,Escherichia coli is the most common pathogens, clinical isolates of Escherichia coli resistant to many kinds of antibiotic in high level.2,An epidemic of qnr-positive and aac(6')-Ib-cr-positive strains in Tianjin is confirmed. This is the first report of qnr mediated quinolone resistance in clinical isolates from Tianjin. The linkage between qnr,aac(6')-Ib-cr and ESBLs was confirmed, and they can spread in vitro level.3,Escherichia colis which carried plasmid-mediated quinolone resistance determinants are mostly multidrug-resistant isolates. The widespread use of antibiotics contributes to the selective pressure for bacterium,which increases the resistance including plasmid-mediated quinolone resistance. |
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