Genetic Characterization of Resistance to Extended-Spectrum β-Lactams in Klebsiella oxytoca Isolates Recovered from Patients with Septicemia at Hospitals in the Stockholm Area

Two β-lactamase gene regions were characterized by DNA sequencing in eight clinical isolates of Klebsiella oxytoca. The bla(OXY-2a) region encoded a β-lactamase nearly identical to OXY-2 (one amino acid residue substituted) and conferred aztreonam and cefuroxime resistance on the K. oxytoca isolates. 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-1a enzyme differed from OXY-1 by two amino acid residues.