In this study, an occurrence of Salmonella enterica in farmed Pangasianodon hypophthalmus was investigated. Salmonella enterica was isolated from the liver and kidney of P. hypophthalmus and characterized using biochemical, antibiogram, hemolysis assays, and whole-genome sequencing. The in- vivo challenge experiment revealed that S. enterica is non-pathogenic to P. hypophthalmus , Labeo rohita , and Oreochromis niloticus. The de novo assembled genome totalled 4,919,008 base pairs with a GC content of 52.06%. The in-silico serotyping identified this strain as S. enterica subsp. enterica serovar Richmond and is potentially pathogenic to humans with a score of 0.9637 out of 1 . The study also identified 127 virulence genes and 66 antimicrobial resistance (AMR) genes.
The PHASTEST analysis for prophage sequences revealed six prophage regions, of which four were intact. The methylated bases across the genome showed that both the lagging and leading strands contained 1.74% methylation from the total Adenine positions present in the sequence. In cytosine methylation, the lagging strand showed 4mC (0.18%), 5mC (1.02%), and 5mCG (0.10%). Similarly, in the leading strand, these values were 4mC (0.16%), 5mC (1.01%), and 5mCG (0.9%). In the case of dam methylation, the lagging strand reported 87.54%, and the leading strand reported 87.73% of methylated bases among the total motifs in the GATC context . Moreover, in the case of dcm methylation, among the total CCAGG motif positions, the lagging strand reported 87.21%, and the leading strand reported 88.33%, respectively.
This work presents the first comprehensive study on S. enterica serovar Richmond isolated from farm-raised fish, highlighting its zoonotic potential for humans.