Genetic and biochemical characterization of FRI-3, a novel variant of the Ambler class A carbapenemase FRI-1.

Abstract

To characterize a new variant of the FRI class A carbapenemase isolated from an MDR clinical Enterobacter cloacae isolate. A carbapenem-resistant E. cloacae was isolated from a rectal swab from a patient in an ICU in Southern Germany. Various phenotypic tests confirmed production of a putative class A carbapenemase. The new bla gene variant, blaFRI-3, and its genetic environment were characterized by WGS. Biochemical characterization was performed by heterologous expression in Escherichia coli TOP10 and by purification of the enzyme with subsequent determination of its kinetic parameters. PCR and sequencing carried out for different class A carbapenemase genes confirmed the presence of a novel variant of blaFRI-1. The novel variant was named FRI-3 and exhibited 91%, 96% and 92% amino acid identity to FRI-1, FRI-2 and FRI-4, respectively. E. coli TOP10 expressing blaFRI-3 showed increased resistance to almost all β-lactams. Comparing the catalytic behaviour of FRI-3 and FRI-1, it was shown that FRI-3 had the same substrate spectrum, but basically hydrolysed β-lactams less efficiently than FRI-1. WGS data revealed that blaFRI-3 was located on a 111 kb plasmid. The biochemical characterization of FRI-3 illustrates that even a few differences in the amino acid sequence can lead to altered catalytic activities of β-lactamases belonging to the same family.