Abstract
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.