Mechanisms involved in carbapenems resistance among isolates of Pseudomonas aeruginosa strains

Abstract number: 1135_36

Kowalska-Krochmal B., Franiczek R., Dolna I, Krzyzanowska B., Litwinek E., Choroszy-Król I., Ruczkowska J.

Objectives:  

The aim of the study was to determine the role of the permeability as well as metalloenzyme production in carbapenems resistant P. aeruginosa strains.

Method:  

Thirty strains of P. aeruginosa determined as resistant to one or two carbapenems (imipenem, meropenem) by disc diffusion (NCCLS) and E-test (AB Biodisk) methods were enrolled in this study. MICs of imipenem (IPM), meropenem (MEM), erythromycin (E), gentamicin (GM), cefoperazone (CFP), norfloxacin (NOR), piperacillin (PIP), tetracycline (T), chloramphenicol (C), EDTA, sodium hexametaphosphate (NaHMP) were determined by agar dilution method according to NCCLS. To estimate the role of the permeability MIC values were also determined in the presence of different concentrations of outer membrane (OM ) permeabilizers: EDTA (0.1 mM, 1 mM, 2.5 mM) and NaHMP (100 mM, 200 mM, 300 mM). Detection of metallo-b-lactamases was performed by disc diffusion method using 2-mercaptopropionic acid and EDTA (as metalloenzyme inhibitors) as well as PCR using specific primers bla IMP1-A 5'- ACC GCA GCA GAG TCT TTG CC -3' and bla IMP1-B 5'- ACA ACC AGT TTT GCC TTA CC-3'.

Results:  

Among 30 P. aeruginosa studied strains 22 were resistant to two carbapenems while 8 were resistant only one of them. Twenty-seven strains were resistant to GM, 26 to T, 18 to NOR, 17 to CFP. EDTA and NaHMP decreased MIC of E from 2- to 32-fold and from 2- to 8-fold, respectively, MIC of GM from 2- to 16-fold and from 2- to 4-fold, MIC CFP from 2- to 64-fold and from 2- to 64-fold, NOR only 2- to 8-fold and 2- and 2-fold, MIC of PIP from 2- to 4-fold and from 2- to 4-fold, MIC of T from 2- to 8-fold and from 2- to 8-fold, MIC of C from 2- to 8-fold and from 2- to 16-fold. Only 1 strain of P. aeruginosa resistant to CFP, 2 strains resistant to PIP and 1 resistant to T became susceptible after treating with EDTA and/or NaHMP. Four of the 30 studied strains were detected to produce metallo-b-lactamases by disc diffusion method. PCR revealed that none of them was carring the bla IMP gene.

Conclusions:  

1. Our results suggest that other metalloenzyme (VIM) are involved in carbapenem-resistance in studied strains. 2. Influence of EDTA and NaHMP on MIC decreased may indicate the role of permeability and efflux mechanisms in carbapenem resistance.