Characterization of NDM-1-Producing Carbapenemase in Proteus mirabilis among Broilers in China

Carbapenem-resistant pathogens mediated by metallo-beta-lactamases (MBLs) have spread worldwide, where NDM-1 is a typical and key MBL. Here, we firstly discussed the distribution characterization of NDM-1, which produces multidrug-resistant Proteus mirabilis among broilers in China. From January to April 2019, 40 (18.1%, 40/221) bla(NDM-1)-carrying P. mirabilis strains were recovered from commercial broilers in slaughterhouse B in China. All the isolates were resistant to imipenem, meropenem and other beta-lactams. These isolates belong to five clusters identified via pulsed field gel electrophoresis (PFGE). Further studies on twenty representative strains revealed that seven bla(NDM-1) genes were located on plasmids with sizes of 104.5-138.9 kb. Notably, only three strains (PB72, PB96 and PB109) were successfully transferred to Escherichia coli J53, while the other four isolates were located in nontransferable plasmids. The rest were harbored in chromosomes. Ulteriorly, based on whole genome sequencing (WGS), these twenty isolates showed four typical phylogenetic clades according to single nucleotide polymorphisms (SNPs) of a core genome and presented four main genomic backbone profiles, in which type II/III strains shared a similar genetic context. All of the above is evidence of bla(NDM)(-1) transmission and evolution in P. mirabilis, suggesting that the prevalence may be more diverse in broiler farms. Accordingly, as intestinal and environmental symbiotic pathogens, bla(NDM-1)-positive P. mirabilis will pose greater threats to the environment and public health.