Bayesian phylogeographic analysis infers cross-border transmission dynamics of drug-resistant Salmonella Enteritidis

Abstract

Salmonella Enteritidis (S. Enteritidis) stands as a leading cause of human salmonellosis worldwide with a tendency to spread through contaminated foodstuffs and animals. In Hong Kong, a significant proportion of food products are imported, and many cases are often caused by the consumption of contaminated food, hence making the geographical surveillance of drug-resistant S. Enteritidis important for strong public health and food safety measures. We analyzed the whole genomes of 207 S. Enteritidis from Hong Kong, Australia, Canada, mainland China, the United States of America, South Africa, Taiwan, and the United Kingdom to examine associated antimicrobial resistance and the transmission dynamics between continents. Phylogenetic cluster inferences and Bayesian phylogeographical analysis were performed. Overall, sequence type ST11 strains were dominant (92.8%, 192/207). Five phylogenomic clusters A to E were identified, where most isolates from mainland China and Hong Kong were in Cluster E. Among the 22 plasmid types identified, IncX1 was dominant in the Asian isolates. Most of the virulence genes were distributed in Salmonella pathogenicity islands −1 and −2, with two universal virulence operons responsible for the effector delivery system and bacterial cell adhesion. The phylogeographic inference analysis showed a statistically significant link between mainland China and Hong Kong with the highest relative migration rate (relativeGeoRates mean ± standard error = 2.93 ± .07, Bayes Factor [BF] = 1285.5], with some traceable to Canada (0.61 ± 0.03, BF = 6.9) and Australia (1.02 ± 0.04, BF = 4.2). Our analysis suggests hypothetical transmission of S. Enteritidis and its associated antimicrobial resistance across borders.