Whole genome sequence-based comparative genomics reveals preliminary genomic features of Salmonella enterica subsp....

Whole Genome Sequencing (WGS) enables detailed characterization of circulating and emerging bacterial strains. Although tens of thousands of Salmonella genomes have been acquired over the years, analyses of the genomic differences between strains of different phage types are scarce.

We compared two Salmonella enterica subsp. enterica serovar Enteritidis (SEn) phage types, namely phage types 1 and 4 from available databases, using bioinformatic tools and nanopore sequencing of a Chilean PT1 strain. Comparisons between the two phage types show very low genomic divergence and high genomic sequence similarity. Single nucleotide polymorphism (SNP) searches identified SNPs specific to each phage type. Although a translocated region was identified in the Chilean PT1 strain analyzed in this study when compared to the genome of a PT4 strain, this was not present in the genomes of other PT1 strains, suggesting a local strain-specific rearrangement. Further analyses yielded no differences in the CRISPR-Cas locus, but a slight difference was observed in Gifsy-2 prophage detection and DNA modification systems between PT1 and PT4 strains.

Our findings provide insights into the genomic differences between SEn strains of two different phage types, serving as a basis for future genomic studies, yet further analyses with more diverse geographical locations collected over a longer time span are essential to validate these differences with the potential to establish molecular markers for strain identification and characterization in the context of epidemiological surveillance as a complement to WGS when this technique is not available.