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 beta-lactamase genes (bla(SHV-11), bla(SHV-1), bla(SHV-26), bla(SHV-32), bla(SHV-36), and bla(SHV-40)) were the most prevalent. Four new variants were identified (bla(LEN-17), bla(OKP-B-13), bla(OKP-B-14), and bla(OKP-A-11)), representing the 1st description of bla(OKP) in the Americas. Among the extended-spectrum beta-lactamase (ESBL) genes, bla(SHV-2), bla(SHV2a), bla(SHV-12), and bla(CTX-M-15) were detected (ESBL prevalence of 0.14%). Nineteen strains were resistant to cefoxitin (MIC, 32 to >256 microg/mL). Nevertheless, an AmpC-like activity was detected in only 1 strain, which expressed CMY-2. The combined effects of narrow-spectrum beta-lactamase production and decreased or nonexpression of OmpK35/36 porins did not account for the cefoxitin resistance observed in some of these strains.