Dissemination of a 'rare' extended-spectrum β-lactamase gene bla mediated by epidemic clones of carbapenemase-producing Enterobacter hormaechei in China.

An increasing trend of the coexistence of a rare extended-spectrum β-lactamase gene bla and carbapenemase genes in Enterobacteriaceae has recently been noted. This study aimed to determine the epidemiological and genetic characterisation of SFO-1-positive carbapenem-resistant Enterobacter cloacae complex (CREC) isolates. A total of 61 CREC clinical isolates were collected in the framework of a national surveillance for carbapenem-resistant Enterobacteriaceae during 2011-2015 in China. Seven SFO-1-positive CREC isolates (11.5%) were identified in four provinces, suggesting a wide dissemination of the bla gene among the CREC population in China. Five SFO-1-positive CREC isolates were further identified by screening 1625 genomes of E. cloacae complex strains retrieved from GenBank. The 12 SFO-1-positive CREC isolates were further identified as Enterobacter hormaechei, of which 10 belonged to epidemic clones (ST93, ST114 and ST418), indicating that these clones might largely contribute to the dissemination of bla. Phylogenomics analysis further identified the occurrence of clonal dissemination in the community setting. The bla-bearing plasmids were assigned to various incompatibility groups with highly diverse sizes (~104-370 kb), suggesting a wide vector range of bla. Two types of genetic context, with and without insertion sequence IS26, were identified for the bla gene. The genetic context flanked by IS26 was more prevalent, thus largely facilitating the mobility of bla. This study revealed that the bla gene is not as rare as previously found and that epidemic clones of CREC are responsible for its dissemination in China. These findings highlight the potential of wide dissemination of low-prevalence antimicrobial resistance genes.