Study Of Pseudomonas Aeruginosa Induced Resistant To Imipenem And Meropenem In Vitro Respectively

Objective:To induce Pseudomonas aeruginosa strains resistant to imipenem and meropenem in vitro. To investingate the susceptibility of routine antibiotics and hypermutation in induced strains.Methods:1. All of strains were identified by MicroScan WalkAway-96 system. The susceptibility of strains to imipenem, meropenem and other antibiotics were determined with routine Kirby-Bauer method, the value of MICs were detected with E-test method.2. The induced tests were adopted low-concentrateion-broth-gene-ration-subculture method. The strains were subcultured in brain-heart infusion broth containing 1/4 concentration imipenem or meropenem at least 25 times. The MICs to imipenem and meripenem were detected with E-test method and the susceptibility to other antibiotics were detected with Kirby-Bauer method in resistant strains respectively.3. The induced strains with different concentration were plated on Luria-Bertani agar supplemented with or without 300ug/ml of rifampin, and the numbers of clones were counted after incubation. Results were indicated as a mean and the mutation frequencies were calculated with standard strain. An isolate was considered hypermutable if the mutateon frequencies after exposure to rifampin was 20 times higher than the mutation frequency of the reference strain.Results:1. In 80 strains of Pseudomonas aeruginosa, 56 strains became resistant to imipenem as the inducement of itself and the rate was 70.0%, and 44 strains were confirmed as the inducement of meropenem and the rate was 55.0%, respectively.2. The MICs of strains to itself of inducing antibiotic were increased in different level after induced. The susceptible rates of imipenem-induced-resistant strains to ceftazidime, cephfime, aztreonam, piperacillin /tazobactam and cefoperazone/sulbactam were 50.0% lower while the rates of meropenem-induced-resistant strains were 70.0% higher. The susceptible rates of imipenem-induced-resistant strains to amikacin and ciprofloxacin were 85.7% and 75.0%, while the rates of meropenem-induced-resistant strains were 100.0% and 80.5%, respectively.3. Twelve hypermutable strains were separated from 56 imipenem-induced-resistant strains and the rate was 21.4%, while six strains from meropenem-induced-resistant strains and the rate was 13.6%.Conclusions:1. Pseudomonas aeruginosa strains can be induced into resistant to imipenem and meropenem by respective antibiotics in vitro. The induced -resistant rate by imipenem was higher than by meropenem obviously.2. The MICs of induced strains to other antibiotics were rising from different level.The decline ratios of susceptibility to beta-lactams and ciprofloxacin in imipenem-induced-resistant strains were higher than in meropenem-induced-resistant strains obviously, but amikacin not different.3. The rate of hypermutant in imipenem-induced-resistant strains was higher than in meropenem-induced-resistant strains obviously.