False susceptibility to cefotetan reported by MicroScan for DHA-type AmpC β-lactamase-producing Klebsiella pneumoniae

Abstract

This study evaluated the accuracy of cefotetan susceptibility determination using the MicroScan WalkAway system for AmpC-producing Klebsiella pneumoniae. In total, 57 K. pneumoniae isolates that showed a D-shape flattening in a double-disk synergy test were studied. Cefotetan MICs were determined by the agar dilution method. The blaDHA gene was detected in all 57 isolates, one of which co-harboured blaCMY-1. According to the MicroScan system, 28 isolates were susceptible, 18 were intermediately-resistant, and 11 were resistant to cefotetan. Compared with the agar dilution method, very major, minor and major error rates were 28.1% (16/57), 47.4% (27/57) and 1.8% (1/57), respectively. © 2007 European Society of Clinical Microbiology and Infectious Diseases.