Phenotypic and Molecular Characterization of an Enterobacter ludwigii Clinical Isolate Carrying a Plasmid-Mediated Gene.

We report a plasmid-encoded IMI-6 carbapenemase in a clinical isolate of Enterobacter ludwigii from Spain. The isolate belongs to ST641 and was susceptible to expanded-spectrum cephalosporins and resistant to carbapenems. The modified carbapenem inactivation method (mCIM) test was positive, but β-Carba was negative. Whole-genome sequencing identified the gene located in a conjugative IncFIIY plasmid and associated with the LysR-like regulator . Both genes were bracketed by an IS-like insertion sequence and a putatively defective IS insertion sequence. IMI carbapenemases confer an unusual resistance pattern of susceptibility to broad-spectrum cephalosporins and piperacillin-tazobactam but decreased susceptibility to carbapenems, which may make them difficult to detect in routine practice. Commercially available molecular methods for the detection of carbapenemases in clinical laboratories do not usually include genes, which could contribute to the hidden dissemination of bacteria producing these enzymes. Techniques should be implemented to detect minor carbapenemases that are not very frequent in our environment and control their dissemination.