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 ( 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 β-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 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.