Diversity of resistance mechanisms in carbapenem-resistant Enterobacteriaceae at a health care system in Northern California, from 2013 to 2016

Abstract The mechanism of resistance in carbapenem-resistant Enterobacteriaceae (CRE) has therapeutic implications. We comprehensively characterized emerging mechanisms of resistance in CRE between 2013 and 2016 at a health system in Northern California. A total of 38.7% (24/62) of CRE isolates were carbapenemase gene-positive, comprising 25.0% (6/24) bla OXA-48 like , 20.8% (5/24) bla KPC , 20.8% (5/24) bla NDM , 20.8% (5/24) bla SME , 8.3% (2/24) bla IMP , and 4.2% (1/24) bla VIM. Between carbapenemases and porin loss, the resistance mechanism was identified in 95.2% (59/62) of CRE isolates. Isolates expressing bla KPC were 100% susceptible to ceftazidime–avibactam, meropenem–vaborbactam, and imipenem–relebactam; bla OXA-48 like –positive isolates were 100% susceptible to ceftazidime–avibactam; and metallo β-lactamase–positive isolates were nearly all nonsusceptible to above antibiotics. Carbapenemase gene-negative CRE were 100% (38/38), 92.1% (35/38), 89.5% (34/38), and 31.6% (12/38) susceptible to ceftazidime–avibactam, meropenem–vaborbactam, imipenem–relebactam, and ceftolozane–tazobactam, respectively. None of the CRE strains were identical by whole genome sequencing. At this health system, CRE were mediated by diverse mechanisms with predictable susceptibility to newer β-lactamase inhibitors.