IBC-1, a novel integron-associated class A beta-lactamase with extended-spectrum properties produced by an Enterobacter cloacae clinical strain

A transferable p-lactamase produced by a multidrug-resistant clinical isola te of Enterobacter cloacae was studied. The bin gene was carried by a large (>80-kb) transmissible plasmid, Nucleotide sequence analysis of cloned fra gments revealed that it was Dart of a gene cassette carried by a class 1 in tegron along with other resistance genes, including aac(6')-lb. The encoded beta-lactamase, designated IBC-1 was a novel class A enzyme that hydrolyze d ceftazidime and cefotaxime and was inhibited by tazobactam and, to a less er extent, by clavulanate, Also, imipenem exhibited potent inhibitory activ ity against IBC-1, The enzyme consisted of 287 amino acid residues, includi ng Ser-237, cysteines at positions 69 and 237a, and Arg-243, which may be i mplicated in its interaction with beta-lactams, In amino acid sequence comp arisons, IBC-1 displayed the highest similarity with the chromosomal penici llinase of Yersinia enterocolitica, a carbenicillinase from Proteus mirabil is GN79, the species-specific beta-lactamases of Klebsiella oxytoca, and th e carbapenemase Sme-1, However, a phylogenetic association with established beta-lactamase clusters could not be conclusively shown.