Recovery of Cephalosporin ResistantEscherichia coliandSalmonellafrom Pork, Beef and Chicken Marketed in Nova Scotia

Abstract

BACKGROUND: Antimicrobial use in farm animals is a potentially important contributor to the emergence of antimicrobial resistance. ResistantSalmonellamay lead to serious human infections and resistantEscherichia colimay transfer plasmid-encoded resistance genes to other pathogens.OBJECTIVE: To determine the prevalence ofE coliandSalmonellaspecies resistant to the third generation of cephalosporins in retail meat products in Halifax, Nova Scotia in 2002.METHODS: Ground beef, ground pork and chicken wings were tested forE coliandSalmonella. E coliwere selected on ceftriaxone-containing media. Beta-lactamases were characterised by isoelectric focusing, polymerase chain reaction and sequencing. Pulsed field gel electrophoresis was performed to determine the relationship of strains. The transferability of plasmids and location of resistance genes was also determined.RESULTS: Forty-three of 75 packages of chicken wings contained ceftriaxone-resistantE coli; 42 of these contained beta-lactamases with isoelectric points at approximately 8.7. Six of seven CMY primer amplicons that were sequenced contained plasmid-mediated Citrobacter freundii-derivedblaCMY-2; the other contained a CMY-2-like beta-lactamase. Pulsed field gel electrophoresis patterns demonstrated that strains were not clonal in nature. Four chicken samples containedSalmonella, one of which containedblaCMY-2-mediated resistance and anE colibearing the same gene, but on different plasmids. Four of 100 beef samples containedblaCMY-2-bearingE coli; none containedSalmonella. Two of 75 pork samples contained ceftriaxone resistantE coli, one of which encoded for CMY-2. One susceptibleSalmonellastrain was recovered from pork.CONCLUSIONS: Chicken from retail outlets located in Halifax, Nova Scotia, commonly containedblaCMY-2-bearingE coli. The relationship antibiotics used in food-producing animals and its effect on resistance of commensals and pathogens needs to be determined.