Prevalence and molecular characterization of carbapenemase-producing gram-negative bacteria from a university hospital in China

Background: The increasing emergence of carbapenem resistance in gram-negative bacteria associated with carbapenemase prompted the initiation of this study. Methods: A total of 3139 gram-negative bacteria were recovered from a 3380-bed university hospital in Wenzhou during 2008 and 2012. Antimicrobial susceptibility was determined using the VITEK2 Compact System and agar dilution method. The phenotype and genotype of carbapenemase were demonstrated using the modified Hodge test, PCR and sequencing. A conjugation experiment was performed to reveal the transferability of resistant genes. The location of the carbapenemase gene was studied by plasmid analysis and southern blot hybridization. Clonal relatedness of the isolates was investigated by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Results: Overall, 751 of 3139 isolates (71/2055 Enterobacteriaceae, 510/620 Acinetobacterbaumannii and 170/464 Pseudomonas aeruginosa) exhibited resistance to carbapenem. Carbapenemase-encoding genes were detected in 70.4% (50/71) of carbapenem-resistant Enterobacteriaceae, including bla(KPC) (80%) and bla(IMP) (20%). All A.baumannii subjected to genotype analysis were positive for bla(OXA-51-like) and co-harboured bla(OXA-23-like) (80.4%) and bla(IMP) (7.8%). ISAba1 was found upstream of bla(OXA-23-like) and bla(OXA-51-like). Eight and seven strains of 170 P. aeruginosa carried bla(IMP) and bla(VIM), respectively. PFGE analysis identified at least one dominant genotype in certain species. Four KPC-2-producing Klebsiellapneumoniae belonged to the same sequence type ST11. The plasmids carrying bla(KPC) were successfully transferred into recipient strains. Conclusion: This study highlights the challenge of increasing prevalence of carbapenem resistance associated with carbapenemase genes and dissemination of epidemic clones in Wenzhou, China.