Mechanisms and molecular typing of carbapenem-resistant Proteus mirabilis strains deficient in swarming motility

Abstract

Objective To investigate the mechanism and epidemiological characteristics of carbapenem-resistant Proteus mirabilis (PM) strains deficient in swarming motility. Methods PM strains were isolated from Hangzhou General Hospital of CAPF (Chinese People′s Armed Police Forces) during January 2013 to December 2014. Bacterial motility and flagella of the PM strains were observed through semi-solid agar culture and flagella staining. Pulsed-field gel electrophoresis (PFGE) was performed for homology analysis. Antimicrobial susceptibility test and phenotypic confirmatory test were also carried out. PCR analysis and DNA sequencing were performed to confirm the genotype of resistant genes. Plasmid electroporation and S1-PFGE in combination with Southern blot hybridization were used to determine the location of the carbapenem-resistant genes. Genetic structure of the blaKPC-2 gene was obtained by PCR mapping. Results A total of 42 PM isolates deficient in swarming motility were screened out and the resistance rates to imipenem and meropenem were 57.1% and 52.4%, respectively. PCR analysis and DNA sequencing confirmed that 24 carbapenem-resistant PM isolates deficient in swarming motility carried blaKPC-2 gene and belonged to three clones as indicated by the results of PFGE. Southern blot hybridization indicated that the blaKPC-2 gene was located on plasmids varying in size (26 kb, 55 kb and 139 kb). In addition, some of the strains harbored several resistant genes, such as blaTEM-1, blaCTX-M-65 and rmtB. The genetic structures of strains carrying blaKPC-2 gene were ISKpn8, blaKPC-2 and ISKpn6-like from upstream to downstream. Conclusion Compared with the PM strains with swarming motility, the carbapenem-resistance rate was significantly higher in these PM strains deficient in swarming motility. Carbapenemases KPC-2 played an important role in the carbapenem-resistant PM strains deficient in swarming motility. There was a cloning spread trend for carbapenem-resistant PM strains in our hospital. Clinicians should pay more attention to the risk of spreading. Key words: Proteus mirabilis; Swarming motility; Carbapenemase; Flagellum; Nosocomial infection