Emergence of mcr-1 and carbapenemase genes in hospital sewage water in Beijing, China

This study identified and characterized mcr-1-positive Enterobacteriaceae (MCRPE) and carbapenemase-producing Enterobacteriaceae (CPE) in hospital sewage water. Influent and effluent sewage samples were collected from five tertiary hospitals in Beijing in December 2016. Samples were screened for MCRPE and CPE using antibiotic selection media. Results were confirmed by PCR amplification of β-lactamase and colistin resistance (mcr-1 and mcr-2) genes and by sequencing. Antimicrobial susceptibility testing, MLST, conjugation and plasmid typing and S1-nuclease-PFGE/Southern blotting were performed for all MCRPE and CPE isolates. Nine MCRPE and 12 CPE isolates were obtained. All mcr-1-positive isolates (n = 9) were Escherichia coli and belonged to eight different STs. The blaKPC-2-positive Enterobacteriaceae included Klebsiella pneumoniae (n = 4), Enterobacter cloacae (n = 4) and Citrobacter freundii (n = 1) isolates. Two C. freundii isolates and one E. cloacae isolate harboured the blaNDM-1 gene. MLST analysis revealed distinct genetic relatedness among all ST11 K. pneumoniae but not among any other carbapenemase-producing isolates. Conjugation and plasmid typing confirmed that three MCRPE isolates harboured mcr-1 on the self-transmissible IncX4 plasmid and the blaNDM-1 gene on the IncX3 plasmid. The sizes of the plasmids harbouring mcr-1, blaNDM-1 and blaKPC-2 were ∼33 to ∼240, ∼40 to ∼75 and ∼30 to ∼90 kb, respectively. To the best of our knowledge, this is the first report of mcr-1-positive E. coli and blaNDM-1-carrying E. cloacae and C. freundii in hospital sewage water. These findings, especially the diversity of MCRPE and K. pneumoniae ST11 that harbour the blaKPC-2 gene, suggest that monitoring and management of hospital sewage water should be enhanced.