Characterization of Canadian cefoxitin-resistant non-typhoidal Salmonella isolates, 2005-06

Abstract

Objectives: Resistance to extended-spectrum cephalosporins has increased in Salmonella worldwide, and is a concern in both hospital and community settings. The aim of this report was to investigate cefoxitin-resistant Salmonella isolates identified from human clinical cases across Canada. Methods: Cefoxitin-resistant isolates, defined as having an MIC ≥ 32mg/L, were screened for the ampC classes DHA, FOX, ENT and CIT in a multiplex PCR followed by sequence analysis. Plasmid analysis by restriction fragment length polymorphism (RFLP) and replicon typing was performed on a convenience sample of cefoxitin-resistant Salmonella. Results: In 2005, 5.3% (181/3442) and in 2006, 3.1% (102/3250) of Salmonella isolates collected from all provinces across Canada displayed cefoxitin resistance. Seventy-one out of 283 (25.1%) were multidrug resistant (MDR), as defined by resistance to at least three different antibiotic classes. The blaCMY-2 gene was harboured by 96.8% (274/283) of the cefoxitin-resistant isolates. Analysis of CMY-2 plasmids revealed that 19.7% contained genes conferring resistance to multiple antimicrobials. Replicon typing of transformant CMY-2 plasmid DNA revealed the predominance of I1-Iγ and A/C. Of the MDR CMY-2 plasmids, 75% contained replicon type A/C. RFLP patterns of CMY-2 plasmids revealed clusters corresponding to the I1-Iγ and A/C replicon types. Conclusions: Incompatibility group I1-Iγ is the most prevalent of the Salmonella CMY-2 plasmids, while A/C is associated with MDR CMY-2 plasmids. © Canadian Crown Copyright 2009. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.