Genetic characterization of resistance to extended-spectrum beta-lactams in Klebsiella oxytoca isolates recovered from patients with septicemia at hospitals in the Stockholm area

Two beta-lactamase gene regions were characterized by DNA sequencing in eig ht clinical isolates of Klebsiella oxytoca. The bla(OXY-2a) region encoded a beta-lactamase nearly identical to OXY-2 (one amino acid residue substitu ted) and conferred aztreonam and cefuroxime resistance on the K. oxytoca is olates. Overproduction of OXY-2a was caused by a G-to-A substitution of the fifth nucleotide in the -10 consensus sequence of bla(OXY-2a). The bla(OXY -1a) was identified in a susceptible strain, and the OXY-la enzyme differed from OXY-1 by two amino acid residues.