FRI-2 carbapenemase-producing Enterobacter cloacae complex in the UK

Objectives: Detection of rarer carbapenemases is challenging, as it requires molecular assays with comprehensive coverage or the use of phenotypic methods for the detection of carbapenemase activity. We describe a new class A carbapenemase, FRI-2, in an Enterobacter cloacae complex isolate following implementation of an in-house multiplex PCR for the detection of 'rare' class A carbapenemases.

Methods: MICs were determined by agar dilution. A carbapenem-resistant E. cloacae complex isolate was tested by PCR for the class A carbapenemases bla KPC , bla FRI , bla IMI , bla GES and bla SME . Carbapenemase activity was assessed using Carba NP and the carbapenem inactivation method. Whole genome and plasmid analyses of the clinical isolate and the FRI-2 transformant were performed by WGS, respectively. Typing was carried out by PFGE.

Results: The E. cloacae complex isolate showed resistance to imipenem (MIC = 16 mg/L), meropenem (MIC = 8 mg/L) and ertapenem (MIC = 8 mg/L), but remained susceptible to piperacillin/tazobactam (MIC = 8 mg/L). Carbapenemase activity was confirmed in the isolate by both phenotypic methods. A bla FRI-1-like gene was detected by PCR and analysis of WGS data of the clinical isolate identified an ORF of 885 bp , which showed 97% nucleotide identity with bla FRI-1 and was named bla FRI-2 . WGS of the transformant indicated bla FRI-2 was located on a 108 kb IncF/IncR plasmid. The FRI-2-positive E. cloacae complex isolate belonged to a novel ST (ST829).

Conclusions: The possible circulation of rarer carbapenemases in clinical settings highlights the role of phenotypic tests to detect carbapenemase activity when molecular assays are negative for the 'big 5' carbapenemase families.