| Objective:Pseudomonas aeruginosa is one of the conditional pathogenic bacteria which commnly caused nosocomial infection, its drug resistance mechanism is very complex, obtaining and expressing metallo-β-lactamases is one of the main mechanisms of PA resistant to carbopenems. The integron-cassette system which has the ability to capture and express foreign genes plays an important role in the fast dissemination of MBLs gene, various drug resistance genes mediated by integron in Pseudomonas aeruginosa are one important reason of multidrug resistance. This topic choosed clinical isolated imipenem-resistant Pseudomonas aeruginosa selected from four rank3-grade A hospitals in Tianjin as the research target, analyzing the drug resistance to common antibacterials of these samples, investigating the prevalence circumstance of MBLs and integron, meanwhile, analyzing the position of the IMP-1gene carried by PA, then ascertain that whether this gene was located on integron. Finally, from the perspective of the expression of blaiMP-1mRNA, discussing the relationship between the production condition of MBLs in PA and resistance to imipenem of PA.Methods:67isolates were collected from four hospitals in Tianjin during January to December in2007, antimicrobial susceptibility test was done by Kirby-Bauer (K-B) test, and compare the drug resistance of them to different antibiotics; metallo-β-lactamases (MBLs) was identified by EDTA-disc synergy test, IMP and VIM MBLs gene were amplified by PCR; class I integrase gene were also amplified by PCR, the PCR product of the variable region was sequenced and analyzed for homology on Genbank, ascertaining the gene cassette carried by the variable region; the position of blaIMP-1was ascertained by PCR; blaIMP-1mRNA expression was checked by Real-time RT-PCR, analyzing the the relationship between the production condition of MBLs and the MIC to imipenem of PA.Results:1.67IRPA were all multidrug resistant isolates, from the results of antimicrobial susceptibility test, the drug resistance circumstance of the trials was critical, the resistance ratio to imipenem and meropenem were nerely100%, the ratio to gentamicin、chloramphenicol and ciprofloxacin exceed70%, the ratio to amikacin were nerely60%, the ratio to ceftazidime and cefoperazone/sulbactam were40%, the ratio to aztreonam were the lowest one, about31%.2.19isolates which carry blaIMP-1were confirmed by PCR in67IRPA, nerely28%; among these19blaIMP-1positive isolates,15isolates has integron-borned IMP-1gene, and these IMP-1gene were co-occur with aadB gene (aminoglycoside resistance) on integron structures.3. In67IRPA,46strains were class Ⅰ integrase gene positive,2of which contained variable region, the variable region of one isolate (PA60) contain aadB and cm1A gene, the sequence of these genes were100%identified with DQ266448; the variable region of another isolate (PA27) contain aac(6’)-Ⅱ cmlA8and OXA-10, which was a new array of gene cassettes, the accession number was EU708817.4. Real-time RT-PCR reflected that, the diference of blamp-1mRNA expression between two groups has statistical significance (P=0.026), blaIMP-1mRNA expression of Group1(lower MIC) were significantly lower than Group2(higher MIC), there may be certain correlation between imipenem resistance and expression of IMP-1.Conclusions:The choice of antibiotics for67IRPA were limited, the resistance ratio to aztreonam and ceftazidime were much lower,31.34and40.30%;19isolates were blcIMP-1positive, most of these IMP-1genes were located on integron, illustrating the significant role of integron in the dissemination of MBLs; Meanwhile, class I integrase gene was existed extensively in IRPA, in addition, this study also found a class1integron carrying new array of gene cassettes in Pseudomonas aeruginosa, indicating the high heterogenicity of integron-cassette system; through the detection of blaIMP-1mRNA expression, illustrating that the higher expression of this gene can influence the MIC to imipenem of PA. |
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