Tracking Salmonella enterica by whole genome sequencing of isolates recovered from broiler chickens in a poultry production system

Salmonella enterica is a major cause of foodborne diseases, and is also an important pathogenic bacterium in poultry industry. Whole genome sequencing (WGS) has become a crucial molecular typing technology used for the surveillance of the pathogenic bacteria. In the present study, we adopted WGS for tracking transmission of S. enterica in the production chain of broiler chickens. A total of 74 S. enterica strains were isolated from the different steps of breeding and slaughtering in a large production enterprise in Sichuan Province, China. The isolation rate of Salmonella was the highest in procedure of defeathering (50.0%) and evisceration (36.7%). Serotype identification showed that 74 Salmonella isolates included 7 serotypes, among which Mbandaka accounted for the highest proportions (35.1%). WGS revealed that 74 strains belonged to 7 different sequence types (STs), as well as 7 different ribosomal STs and 35 core genome STs. cgMLST-based Minimum Spanning Trees and phylogenetic tree based on the SNPs indicated that three serotypes, Mbandaka, Indiana and Kentucky, could be clonally transmitted between broiler farm and slaughterhouse. Heterogeneous resistant phenotypes and genotypes were found in two serotypes, Indiana and Kentucky. Our study indicated WGS in an accurate tool for molecular typing of S. enterica. Routine surveillance of S. enterica in the production chain of broiler chickens is needed.