CONTEXT Isolation and characterization of OXA-162, a novel variant of OXA-48. OBJECTIVES Klebsiella pneumoniae isolate with decreased susceptibility to carbapenems was recovered from a Turkish patient. This study aimed at characterizing the carbapenem resistance determinants of this isolate. MATERIALS AND METHODS Antibiotic susceptibility tests, analytic isoelectric focusing (IEF), cloning and sequencing were performed. Cloned β-lactamase was purified by means of preparative gel electrophoresis and the kinetic constants were determined under initial rate conditions. RESULTS The identified bla(OXA-162) gene was located on a ca. 45-kb plasmid carrying a transposon consisted of two IS1999-2 elements. OXA-162 differed from OXA-48 by a single amino acid substitution (Thr213Ala) which increased the catalytic efficiency (k(cat)/K(M)) of OXA-162 towards imipenem and meropenem. Also this substitution caused a gain of hydrolysis ability towards doripenem. Analysis of OXA-162 model implied that the amino acid change might generate an extension in the opening of the substrate entry site and might cause extended hydrolytic activity towards imipenem, meropenem and doripenem. DISCUSSION AND CONCLUSION OXA-162, a derivative of OXA-48 has enhanced catalytic properties.