Surveillance and characterization of carbapenem-resistant Enterobacter cloacae complex from China, 2015-2018

The carbapenem-resistant Enterobacter cloacae (CREC) have become a global health concern. However, our understanding of its epidemiological trends and resistance mechanisms still needs to be improved.

Ninety-one non-repetitive clinical CREC isolates were collected from 12 hospitals across China and identified using MALDI-TOF MS, rMLST, ANI, MASH, and dDDH. Minimal inhibitory concentrations were determined via broth microdilution. Resistance genes and plasmid replicons were identified using ResFinder and PlasmidFinder. Carbonyl cyanide 3-chlorophenylhydrazone suppression test and OmpC and OmpF overexpression test were conducted on 32 non-carbapenemase-producing (NCP) isolates. A phylogenetic tree was constructed with kSNP4 and visualized through iTOL.

Among the 91 CREC isolates, E. hormaechei was predominate (75 isolates), followed by E. kobei (five isolates). Within E. hormaechei, E. hormaechei subsp xiangfangensis was the most widespread subspecies. Sixty isolates produced carbapenemase, with bla_NDM-1 identified in 36 isolates, bla_KPC-2 in six isolates, and bla_NDM-5 in six isolates. Two isolates harbored both bla_NDM-1 and bla_KPC-2. Thirty-two isolates were NCP isolates, primarily due to carbonyl cyanide 3-chlorophenylhydrazone suppression.

Among CREC in China, the bla_NDM-1 was the dominant carbapenemase-coding gene. For NCP isolates, efflux pumps were the main reason for carbapenem resistance, and susceptibility could be restored in an antibiotic-free environment.