Analysis on genetic homology and metallo--lactamase genes of imipenem-resistant Pseudomonas aeruginosa clinical isolates

Objective To investigate the genetic homology and carriage of metallo--lactamase genes of imipenem-resisitant Pseudomonas (P.) aeruginosa isolated in Dalian, Liaoning province. Methods A total of 400 clinical isolates of P. aeruginosa were collected from four hospitals in Dalian during January 2013-September 2014. After the isolate identification, the drug susceptibility test was conducted following the standard protocol of Clinical and Laboratory Standards Institute (CLSI). E-test (IPM/EDTA) was dione to detect metallo--lactamase gene phenotype, PCR was applied to detect MBL genes, and pulsed-field gel electrophoresis (PFGE) was performed for homology analysis. Results Eighty-nine imipenem-resistant P. aeruginosa strains were identified through drug susceptibility test, most of which showed multi-resistance. Among the 89 strains, only 17 strains screened by E-test were proved to be metallo--lactamase positive (19.11%); 11 strains carried metallo--lactamase genes, in which 8 strains carried IMP-1 gene and 3 strains carried VIM-2 gene; A total of 15 different PFGE types (A-O) were identified with 46 strains in type A, 16 in type B,4 in type C,5 in type D,4 in type E,3 in type F, 2 in type G, 2 in type H, 1 each in type I-O. The P. aeruginosa belonging to PFGE type A-G were mainly collected from 4 hospitals, which were gene diversity, but the strains in each type shared 100% homology. Conclusion This study showed that the drug resistance of P. aeruginosa is serious in Dalian. The hydrolyzing effect of the metallo--lactamase is one of the main resistance mechanism of P. aeruginos to imipenem,the major genotypes were IMP-1 and VIM-2. The result of PFGE suggested that outbreak has not yet occurred in this area. PFGE can be used in the source tracing and molecular epidemiological study of drug resistance and homology of the pathogens.