Salmonella enterica
(SE) can survive in surface waters (SuWa) and the role of non-host environments in its transmission has acquired increasing relevance. In this study, we conducted comparative genomic analyses of 172 SE isolates collected from SuWa across three months in six states of central Mexico during 2019. SE transmission dynamics were assessed using 87 experimental and 112 public isolates from Mexico collected during 2002-2019. We also studied genetic relatedness between SuWa isolates and human clinical strains collected in North America during 2005-2020. Among experimental isolates, we identified 41 SE serovars and 56 multi-locus sequence types (ST). Predominant serovars were Senftenberg (n=13), Meleagridis, Agona, and Newport (n=12 each), Give (n=10), Anatum (n=8), Adelaide (n=7), and Infantis, Mbandaka, Ohio and Typhimurium (n=6 each). We observed a high genetic diversity in the sample under study, as well as clonal dissemination of strains across distant regions. Some of these strains are epidemiologically important (ST14, ST45, ST118, ST132, ST198, and ST213), and were genotypically close to those involved in clinical cases in North America. Transmission network analysis suggests that SuWa are a relevant source of SE (0.7 source/hub ratio) and contributes to its dissemination as isolates from varied sources and clinical cases have SuWa isolates as common ancestors. Overall, the study shows SuWa act as reservoir of various SE serovars of public health significance. Further research is needed to better understand the mechanisms involved in SuWa contamination by SE, as well as develop interventions to contain its dissemination to food production settings.
Study importance
Surface waters are heavily used in food production worldwide. Several human pathogens can survive in these waters for long periods and disseminate to food production environments, contaminating our food supply. One of these pathogens is
Salmonella enterica
, a leading cause of foodborne infections, hospitalizations and deaths in many countries. This research demonstrates the role of surface waters as a vehicle for the transmission of
Salmonella
along food production chains. It also shows some strains circulating in surface waters are very similar to those implicated in human infections and harbor genes that confer resistance to multiple antibiotics, posing a risk to public health. The study contributes to expand our current knowledge on the ecology and epidemiology of
Salmonella
in surface waters.