Contribution of OprD2 Expression and Metallo-β-lactamases in Imipenem Resistance of Pseudomonas aeruginosa Clinical Isolates

OBJECTIVE To investigate the possible contribution of OprD expression and metallo-β-lactamases(MBLs) in Pseudomonas aeruginosa clinical stains resistant to imipenem.METHODS Clinical strains resistant to imipenem were screened for MBLs production by a disk diffusion synergy test and subjected to PCR assays with primers specific for MBLs.Sequence analysis was provided to identify the prevalence of MBLs gene.Biochemical properties of MBLs were determined by β-lactamase assays with crude preparations of β-lactamases.Expression of OprD2 was determined by quantitative RT-PCR and Western blot analysis.RESULTS Among 128 imipenem resistant strains,7(5.4%) and 10(7.8%) isolates were positive for VIM-2 and IMP-1 genes,respectively.Crud extraction of β-lactamases showed imipenem-hydrolyzing activity and could be inhibited by treatment with EDTA.In these imipenem-resistant clinical isolates,OprD2 protein was low-expressed in 10 isolates(7.8%) and normally expressed in 12 isolates(9.3%) but not expressed in 106 isolates(83.3%).However,17 isolates(13.3%) of MBLs producing strains were all lack of OprD2 expression.CONCLUSIONS Reduced or lack of OprD2 expression is the essential mechanisms for most imipenem-resistant clinical isolates of P.aeruginosa.blaVIM-2 And blaIMP-1 are prevalent in P.aeruginosa clinical resistant strains and may lead to nosocomial infection.