|
Background & ObjectivePseudomonas aeruginosa is a common clinical conditioned pathogens, which are widely distributed in nature and healthy skin, intestinal and respiratory tract. Pseudomonas aeruginosa often infects immunocompromised patients and nosocomial infections caused by it has become more than 30%. Since Pseudomonas aeruginosa is tolerated and broad spectrum resistance, and also shows a wide range of natural or acquired resistance to several antimicrobial agents, the choice of the effective antibiotics which are due to infection is less. The extensive and irrational use of antimicrobial agents, makes the resistance of Pseudomonas aeruginosa becoming stronger. There has been a lot of multidrug resistant strains which resistant to imipenem and commonly used drugs in anti-Pseudomonas, which makes the clinical treatment great difficult. In view of the main reasons is its multidrug resistance, and resistance mechanisms being more complex, it is difficult to eradicate infection caused by Pseudomonas aeruginosa, especially imipenem-resistant Pseudomonas aeruginosa. On the other hand, the number of hospital infections is increasing, and outbreaks of multiple drug-resistant strains caused by nosocomial infection sometimes occur, which bring serious damage to patients, hospitals and community. In order to understand the multiple drug resistance and resistance mechanisms of imipenem-resistant Pseudomonas aeruginosa in the region, we used broth microdilution method and polymerase chain reaction (PCR) to detect the resistant phenotype and genotype of imipenem-resistant Pseudomonas aeruginosa in this study. To define whether the strains of the infection are homologous and determine the infection is sporadic or epidemic outbreaks, we use drug resistance gene typing (DRGT) and pulsed-field gel electrophoresis (PFGE) to make the phylogenetic analysis of imipenem-resistant Pseudomonas aeruginosa in this region, which provide a theoretical basis for the prevention and control of hospital infection in the region. MethodsDuring January 2008 to January 2009, a total of 384 Pseudomonas aeruginosa, of which 72 strains were imipenem-resistant Pseudomonas aeruginosa, isolated by the clinical microbiology laboratory of four branches of the Traditional Chinese Hospital of Guangdong Province, of which 72 strains were resistant to imipenem. All strains were identified by the VITEK2 automatic identification system of Merieux of French. The disk diffusion method was performed in 384 Pseudomonas aeruginosa and the minimum inhibitory concentrations (MICs) of 12 antibiotics that are commonly used in clinic were determined by broth microdilution method in 72 imipenem-resistant Pseudomonas aeruginosa. PCR for detection of resistant genes intIl, OprD2, GES, KPC, IMP-1, IMP-9, VIM-1, VIM-2, SIM, SPM, GIM, AIM, NDM, KHM, DHA, PDC, OXA-40, OXA-23 was performed. DRGT was based on the results of resistance genes of PCR. Pulsed-field gel electrophoresis (PFGE) of 72 Pseudomonas aeruginosa isolates were performed. Results(1) The resistance rates of 384 Pseudomonas aeruginosa isolates to ciprofloxacin and ticarcillin were the highest, both 39.9%; the resistance rates to imipenem and meropenem were 18.8% and 18.5%.(2) There are 72 nonduplicated imipenem-resistant Pseudomonas aeruginosa isolates in this study,100% of which were multidrug-resistant isolates.12 antimicrobial resistance rates were greater than 50%, which was significantly higher than 384 Pseudomonas aeruginosa isolates.72 imipenem-resistant Pseudomonas aeruginosa isolates are resistant to a wide range of antibiotics and have high level of resistance. In addition to meropenem, cefepime, piperacillin-tazobactam and cefoperazone-sulbactam, the number of isolates whose MIC results of other antibiotics were more than four times of break point value were more than 50% of the strains. Though the type and quantity of genes were different in the imipenem-resistant Pseudomonas aeruginosa isolates, the level of resistance to antibiotics was the same.(3) The IntIl, OprD2, IMP-1, IMP-9, VIM-2, SIM, AIM, NDM, DHA and PDC genes were detected in 100.0%,86.1%,2.8%,9.7%,70.8%,13.9%,1.4 %,2.8%,1.4%,18.1% and 98.6% by PCR amplification. The GES, VIM-1, SPM, GIM, KHM, OXA-40, OXA-23 genes were not detected. In this study, the type and quantity of genes carried by imipenem-resistant Pseudomonas aeruginosa resistance are different, but the level of resistance to antibiotics is more consistent.(4) Seventeen different PFGE types, designated from A to Q, were distinguished among the 72 imipenem-resistant Pseudomonas aeruginosa isolates. Of these 72 isolates,40 clustered as the same type, designated type A. Six isolates designated type B, six designated type C, five designated type C, five designated type D, each of two designated type E and F, one designated type G to Q respectively. After checking the sources of the strains of type A to type F, we found that the strains of each type were from different hospitals and different times, which did not constitute an outbreak. The result of DRGT showed that 72 Pseudomonas aeruginosa isolates can be divided into three groups, and there is clonal dissemination in every group, for example, A group 3-5-11-13-16-17-18-19-22-23-24-25-31-36-40-41-46-47-50-59-60-65-69-70-71-85 isolates,2-6-7-8-9-10-12-14 isolates,1-15-33-37-38-43-45-53-55-57-62-64-78-81-83 isolates,42-44-51-58-61 isolates,29-30 isolates,28-32-34 isolates; B group 48-54-66-82 isolates; C group 27-V2 isolates. The isolates clustered as the same group by DRGT were divided into different type by PFGE. Conclusions72 imipenem-resistant Pseudomonas aeruginosa isolates of the region all have multidrug resistance and high level of resistance. The level of resistance is not only related to the type and quantity of genes, but also to the expression of genes. Imipenem resistance of these 72 isolates is most closely related to the production of metallo-β-lactamase. The emergence of new metallo-β-lactamase types SIM, AIM amd NDM indicates that the mechanisms of bacterial resistance become more and more complex. The result of PFGE suggests that outbreak has not yet occurred in this region, but there are popular advantage clones. Therefore it required to monitor drug resistance actively cooperating with hospital infection control department, to prevent hospital infection and outbreak. Compared to PFGE and DRGT, both of them have their own advantages, we should select the appropriate classification to monitor based on clinical needs.
|