Cephalosporin resistance in Klebsiella pneumoniae from Nova Scotia, Canada

From 2116 Klebsiella pneumoniae strains isolated between January 2001 and December 2002 in Nova Scotia, Canada, 25 (1.18%) showed a reduced susceptibility to cefoxitin or extended-spectrum cephalosporins. Narrow-spectrum β-lactamase genes (blaSHV-11, blaSHV-1, blaSHV-26, blaSHV-32, blaSHV-36, and blaSHV-40) were the most prevalent. Four new variants were identified (blaLEN-17, blaOKP-B-13, blaOKP-B-14, and blaOKP-A-11), representing the 1st description of blaOKP in the Americas. Among the extended-spectrum β-lactamase (ESBL) genes, blaSHV-2, blaSHV2a, blaSHV-12, and blaCTX-M-15 were detected (ESBL prevalence of 0.14%). Nineteen strains were resistant to cefoxitin (MIC, 32 to >256 μg/mL). Nevertheless, an AmpC-like activity was detected in only 1 strain, which expressed CMY-2. The combined effects of narrow-spectrum β-lactamase production and decreased or nonexpression of OmpK35/36 porins did not account for the cefoxitin resistance observed in some of these strains.