Study On Metallo-β-lactamase In Imipenem-resistant Pseudomonas Aeruginosa

Metallo-p-lactamases (MBL) cause serious problem for clinical treatment. MBL belonged to classes B by Ambler molecular classification.The substrates of MBL include penicilin, cephalosporins and carbapenems. Pseudomonas aeruginosa,also called "pseudomonas pyocyanea",is a common pathogen of nosocomial infection. The resistance of the P.aeruginosa become more serious as β-lactams, immuno-suppressive drugs and anti-neoplasm drugs were widely used in clinical recently. Four types of MBL(IMP,VIM, SPM-1 and GIM-1) had been reported in P.aeruginosa.We carried out this study to demonstrate the drug resistance and the genotyping of imipenem-resistant Pseudomonas aeruginosa (IRPA). 140 strains of IRPA were isolated from hospitals in five areas of China. The minimal inhibitory concentration (MIC) of the strains to ten kinds of antimicrobial agents were determined by Etest and agar dilution method. MBL were detected by disk diffusion test. PCR was performed to amplify the sequences of the MBL and integron genes. Conjugation experiment, Southern hybridization , plasmid extraction and electrotransformation were carriedout for the location of MBL genes. Pulsed-field gel electrophoresis(PFGE) was used to analyze the homology of the MBL producing strains.MBLs were detected to be positive in 12 strains by disk diffusion test, while VIM-2 gene was positive in 14 strains by PCR. Two kinds of integron were detected from 12 of these 14 strains. One contained aacA4, blaVIM-2 and another contained aacA4, blaVIM-2 and aadB cassettes. It was failed to transfer the MBL gene by conjugation and electrotransformation tests repeatedly. Seven different PFGE types were found among 14 strains. The VIM-2 probe hybridized with a 50kb Xbal fragment by Southern hybridization.In brief, the positive rate of MBL-producing strains among imipenem resistance P. aeruginosa isolates from five areas of China was 10.0%. All of the MBL gene types were VIM-2 . The blaVIM-2 gene cassettes located in different class 1 integrons .The strains from different areas had different PFGE types.