Surveillance Of Antimicrobial Agents Resistance And Investigation On Mechanism Of Imipenem-resistance Of Pseudomonas Aeruginosa

Objective:To investigate the resistance to 15 antimicrobial agents about 236 strains of P.aeruginosa collected in Center for Surveillance of Bacterial Resistance of Anhui Province and guide rational use of antimicrobial agents to clinical therapy.To study the mechanism of 14 imipenem-resistant P. aeruginosa isolated from clinical patients.Materials and Methods:Totally 236 clinical isolates of P. aeruginosa were collected from 34 hospitals of Anhui province in 2006. M-H agar dilution method was used to detect the minimal inhibitory concentration (MIC) of 15 antimicrobial agents against wild-type isolates through referring antimicrobial agents susceptibility standards of CLSI 2006.Metallo-beta-lactamase was screened by disc synergy test, PCR methods was employed to examine the genes of IMP-1, IMP-2, VIM-1, VIM-2, SPM metallo-beta-lactamase and outer membrane encoded by OprD gene. Carbonyl cyanide 3-chlorophenylhydrazone(CCCP) was used to study the affection on the MIC of imipenem and active efflux pumps system in 14 imipenem-resistant P. aeruginosa. Results:155 strains (65.7%) were seprated from Sputum and respiratory secretions. In vitro sensceptibility tests of 15 antimicrobial agents, higher susceptibility were obtained with meropenem (90.3%), imipenem (88.6%), piperacillin / tazobactam (78.0%), aamikacin (64.4%), nd ceftazidime (64.0%) respectively. Higher resistances were obtained with cefuroxime (98.3%), ceftriaxone (77.9%), cefotaxime (71.6%), aztreonam (59.7%), and cefoxitin (59.2%) respectively.The 14 strains of imipenem-resistant P. aeruginosa are severely resistant to other 14 antimicrobial agents, the multi-resistant rate is 100%. 5 strains of metallo-beta- lactamase-producing were positive for VIM-2 gene as same as the disk synergy test founded. Ohers genes of metallo-beta-lactamase aren't found. OprD gene was negative in 11 strains. 2 strains had active efflux pumps system because their MICs to imipenem were cut down to 1/4 affected by CCCP.Conclusion:155 strains of P. aeruginosa (65.7%) were seprated from sputum and respiratory secretions which could cause the infections of respiratory tract. In vitro antimicrobial sensitivity test against clinical isolates of 236 strains P. aeruginosa, most of the resistant rates are high and more common phenomenon of multi-drug resistance in 15 kinds of commonly used clinical antimicrobial agents. cefuroxime, ceftriaxone, cefotaxime, aztreonam, and cefoxitin are not selected to treat clinical infections caused by P.aeruginosa. At present carbapenem was the first choice to the treatment of infections caused by P.aeruginosa, the followed is including inhibitors ofβ-lactam and cephalosporin or assoiating with aminoglycoside when conditions permit. According to antimicrobial sensitivity tests results to select a reasonable choice of antimicrobial agents was an effective means to control the resistant P. aeruginosa. The loss of outer membrane OprD2 was the first reason to imipenem-resistant P. aeruginosa. The second reasons were metallo-beta-lactamase and active efflux pumps systems. Metallo-beta-lactamase was detected by disc synergy test which was an accurate, easy, economic, easy operating method. In addition, two kinds resistant mechanism were found in 4 strains(93,125,433,1451) of 14 strains imipenem-resistant P.aeruginosa.