Search

Extended-spectrum β-lactamases (ESBLs) confer resistance to extended-spectrum cephalosporins, a major class of clinical antimicrobial drugs. We used genomic analysis to investigate whether domestic food animals, retail meat, and pets were reservoirs of ESBL-producing Salmonella for human infection in Canada. Of 30,303 Salmonella isolates tested during 2012-2016, we detected 95 ESBL producers. ESBL serotypes and alleles were mostly different between humans (n = 54) and animals/meat (n = 41). Two exceptions were bla SHV-2 and bla CTX-M-1 IncI1 plasmids , which were found in both sources. A subclade of S. enterica serovar Heidelberg isolates carrying the same IncI1-bla SHV-2 plasmid differed by only 1-7 single nucleotide variants. The most common ESBL producer in humans was Salmonella Infantis carrying bla CTX-M-65 , which has since emerged in poultry in other countries. There were few instances of similar isolates and plasmids, suggesting that domestic animals and retail meat might have been minor reservoirs of ESBL-producing Salmonella for human infection.

We investigated whether the increased prevalence of gentamicin resistance in Salmonella from human infections was related to a similar increased prevalence in isolates from broiler chickens and whether this increase may have been due to coselection from use of lincomycin-spectinomycin in chickens on farms. Whole-genome sequencing was performed on gentamicin-resistant (Gen r ) Salmonella isolates from human and chicken sources collected from 2014 to 2017 by the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS). We determined the genomic relatedness of strains and characterized resistance genes and plasmids. From 2014 to 2017, 247 isolates of Gen r Salmonella were identified by CIPARS: 188 were from humans, and 59 were from chicken sources (26 from live animals on farm and 33 from retail meat). The five most common Gen r serovars were Salmonella enterica serovars Heidelberg ( n  = 93; 31.5%), 4,[5],12:i:- ( n  = 42; 14.2%), Kentucky ( n  = 37; 12.5%), Infantis ( n  = 33; 11.2%), and Typhimurium ( n  = 23; 7.8%). Phylogenomic analysis revealed that for S. Heidelberg and S. Infantis, there were closely related isolates from human and chicken sources. In both sources, resistance to gentamicin and spectinomycin was most frequently conferred by aac(3)-VIa and ant(3 '' )-Ia , respectively. Plasmid closure confirmed linkages of gentamicin and spectinomycin resistance genes and revealed instances of similar plasmids from both sources. Gentamicin and spectinomycin resistance genes were linked on the same plasmids, and some plasmids and isolates from humans and chickens were genetically similar, suggesting that the use of lincomycin-spectinomycin in chickens may be selecting for gentamicin-resistant Salmonella in broiler chickens and that these resistant strains may be acquired by humans.