Pan genome clustering identifies a novel mosaic prophage specific to Salmonella Enteritidis lineage associated with the invasive disease in India.

Abstract

Salmonella enterica serovar Enteritidis is a leading cause of invasive non-typhoidal Salmonella (iNTS) disease globally, particularly in sub-Saharan Africa. In contrast, the epidemiology and population structure of invasive S. Enteritidis in South Asia remain poorly characterized. This study investigates the clinical presentation, phylogenetic relationships and genomic characteristics of S. Enteritidis bloodstream infections (BSIs) in India. Clinical data were collected from 101 patients with S. Enteritidis BSI between 2012 and 2022. Whole-genome sequencing was performed on representative bloodstream isolates together with isolates from non-blood clinical specimens and poultry sources. Comparative genomic analyses included phylogenetic reconstruction, invasiveness index prediction, and prophage characterization. Infants and immunosuppressed individuals were disproportionately affected by iNTS disease. Phylogenetic analysis identified four major lineages of S. Enteritidis. Most BSI isolates clustered in a previously unrecognized lineage, designated the Global Intermediate Clade, which occupied a phylogenetic position between the Global outlier and Global epidemic clades. Bayesian inference dated its most recent common ancestor to around 1789 AD (95% HPD: 1692-1941), with global circulation confirmed by European and Asian isolates. The Global Intermediate clade exhibited the second-highest invasiveness index (median 0.221, SD 0.013) after the West African clade; however, this index reflects genomic signatures associated with invasiveness and should not be interpreted as a direct measure of virulence. Poultry isolates clustered separately from the dominant bloodstream-associated lineage. Pan-genome analysis identified a lineage-specific mosaic prophage composed of modules homologous to prophages found in diverse Enterobacterales. This study provides the first detailed genomic insight into invasive S. Enteritidis in India and identifies a previously unrecognized Global Intermediate Clade associated with bloodstream infection. The distinct phylogenetic placement and genomic features of this lineage, including a lineage-specific mosaic prophage, warrant further investigation and support the need for expanded One Health genomic surveillance.