Genomic analysis of Salmonella enterica serovar Typhimurium from wild passerines in England and Wales

Passerine salmonellosis is a well-recognized disease of birds in the order Passeriformes, which includes common songbirds such as finches and sparrows, caused by infection with Salmonella enterica serovar Typhimurium. Previous research has suggested that some subtypes of S. Typhimurium—definitive phage types (DTs) 40, 56 variant, and 160—are host adapted to passerines and that these birds may represent a reservoir of infection for humans and other animals. Here, we have used the whole-genome sequences of 11 isolates from British passerines, five isolates of similar DTs from humans and a domestic cat, and previously published S. Typhimurium genomes that include similar DTs from other hosts to investigate the phylogenetic relatedness of passerine salmonellae to other S. Typhimurium isolates and investigate possible genetic features of the distinct disease pathogenesis of S. Typhimurium in passerines. Our results demonstrate that the 11 passerine isolates and 13 other isolates, including those from nonpasserine hosts, were genetically closely related, with a median pairwise single nucleotide polymorphism (SNP) difference of 130 SNPs. These 24 isolates did not carry antimicrobial resistance genetic determinants or the S. Typhimurium virulence plasmid. Although our study does not provide evidence of Salmonella transmission from passerines to other hosts, our results are consistent with the hypothesis that wild birds represent a potential reservoir of these Salmonella subtypes, and thus, sensible personal hygiene precautions should be taken when feeding or handling garden birds.