In a collaboration between Soochow (China), Institut Pasteur (Shanghai), CDC (China), Liverpool, Georgia (US), and Warwick we investigated the host-specificity of S. enterica based on 362,931 publically accessible genomes in EnteroBase (a database of sequenced enteric bacteria genomes hosted and developed at Warwick). We detected the presence of nine populations that are enriched in pigs and observed frequent intercontinental transmission of genetically almost identical strains in these pig-enriched populations, which cannot be explained solely by natural causes. Therefore, we focused on one population enriched in pigs, serovar Choleraesuis, reconstructing the historical fluctuations in this population, accumulation of antimicrobial-resistant genes, and international transmissions. We revealed a 2-stage expansion in the population of this serovar, the first associated with the development of intensive pig farming in the early 20th century and the second due to the increased frequency of antimicrobial resistance after the 1960s. Additionally, we found that Europe and the USA contributed the most to international transmissions of this serovar.
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