Purpose: The objective of this study was to analyze the antibiotic resistance phenotype and genotype of Salmonella isolated from broilers in Canadian production systems.
Methods: A total of 194 Salmonella isolates recovered from a large commercial farm in British Columbia, Canada, were speciated and serotyped. Susceptibility to antibiotics was performed by Sensititre. Detection of virulence and antibiotic resistance genes was performed by PCR. Genetic diversity was determined by pulse-field gel electrophoresis typing (PFGE).
Results: Seventeen different serovars of Salmonella were identified. The most prevalent included Kentucky (29.4%), Typhimurium (15.5%), Enteritidis (13.9%), Hadar (12.4%), while 15 Heidelberg, 10 Enterica, 9 Brandenburg and 7 Thompson isolates were also recovered. Overall, resistance to ampicillin (45.7%), amoxicillin-clavulanic acid (43.2%), ceftiofur (42.6%) cefoxitim (41.6%), tetracycline (29.4) and streptomycin (21.3%) was most common. Thirty-three (57.9%) of the serovar Kentucky isolates were resistant to amoxicillin-clavulanic acid-ampicillin-cefoxcitin-ceftiofur, and two isolates were also resistant to chloramphenicol, streptomycin, sulfisoxazol and tetracycline. Genes associated with resistance to aminoglycoside (aadA1, aadA2, strA), β-lactam (CMY-2, SHV, TEM), tetracycline (tetA and tetB) and sulfonamide (sul1) were detected in all 194 isolates. The invasin (invA) and virulence (spv) genes were found in 63.4% and 7.7% of the isolates, and 10 of the 27 (37.0%) S. Enteriditis carried both invA and spv. PGFE typing revealed that the antibiotic resistant serovars were genetically diverse.
Significance: The data confirmed that broiler chickens are colonized by genetically diverse antibiotic resistant Salmonella harboring virulence determinants. The presence of such strains is highly relevant to food safety and public health.