Enterobacter cloacae Complex Isolates Harboring bla NMC-A or bla IMI -Type Class A Carbapenemase Genes on Novel Chromosomal Integrative Elements and Plasmids

Abstract

Carbapenem-resistant Enterobacter cloacae complex isolates submitted to a reference laboratory from 2010 to 2015 were screened by PCR for seven common carbapenemase gene groups, namely, KPC, NDM, OXA-48, VIM, IMP, GES, and NMC-A/IMI. Nineteen of the submitted isolates (1.7%) were found to harbor Ambler class A bla _NMC-A or bla _IMI -type carbapenemases. All 19 isolates were resistant to at least one carbapenem but susceptible to aminoglycosides, trimethoprim-sulfamethoxazole, tigecycline, and ciprofloxacin. Most isolates (17/19) gave positive results with the Carba-NP test for phenotypic carbapenemase detection. Isolates were genetically diverse by pulsed-field gel electrophoresis macrorestriction analysis, multilocus sequence typing, and hsp60 gene analysis. The genes were found in various Enterobacter cloacae complex species; however, bla _NMC-A was highly associated with Enterobacter ludwigii . Whole-genome sequencing and bioinformatics analysis revealed that all NMC-A ( n = 10), IMI-1 ( n = 5), and IMI-9 ( n = 2) producers harbored the carbapenemase gene on EludIMEX-1-like integrative mobile elements (EcloIMEXs) located in the identical chromosomal locus. Two novel genes, bla _IMI-5 and bla _IMI-6 , were harbored on different IncFII-type plasmids. Enterobacter cloacae complex isolates harboring bla _NMC-A/IMI -type carbapenemases are relatively rare in Canada. Though mostly found integrated into the chromosome, some variants are located on plasmids that may enhance their mobility potential.