Pathogenic potential of non-typhoidal Salmonella serovars isolated from aquatic environments in Mexico.

Background: River water has been implicated as a source of non-typhoidal Salmonella (NTS) serovars in Mexico.

Objective: To dissect the molecular pathogenesis and defense strategies of seven NTS strains isolated from river water in Mexico.

Methods: The genome of Salmonella serovars Give, Pomona, Kedougou, Stanley, Oranienburg, Sandiego, and Muenchen were sequenced using the whole-genome shotgun methodology in the Illumina Miseq platform. The genoma annotation and evolutionary analyses were conducted in the RAST and FigTree servers, respectively. The MLST was performed using the SRST2 tool and the comparisons between strains were clustered and visualized using the Gview server. Experimental virulence assay was included to evaluate the pathogenic potential of strains.

Results: We report seven high-quality draft genomes, ranging from ~ 4.61 to ~ 5.12 Mb, with a median G + C value, coding DNA sequence, and protein values of 52.1%, 4697 bp, and 4,589 bp, respectively. The NTS serovars presented with an open pan-genome, offering novel genetic content. Each NTS serovar had an indistinguishable virulotype with a core genome (352 virulence genes) closely associated with Salmonella pathogenicity; 13 genes were characterized as serotype specific, which could explain differences in pathogenicity. All strains maintained highly conserved genetic content regarding the Salmonella pathogenicity islands (1-5) (86.9-100%), fimbriae (84.6%), and hypermutation (100%) genes. Adherence and invasion capacity were confirmed among NTS strains in Caco-2 cells.

Conclusion: Our results demonstrated the arsenal of virulence and defense molecular factors harbored on NTS serovars and highlight that environmental NTS strains are waterborne pathogens worthy of attention.