E49 - Impact of the Fecal Microbiome on Subclinical Salmonella Shedding in Horses

Abstract: Background: Subclinical shedding of Salmonella in horses is more common than clinical disease and more likely to go undetected, posing a persistent biosecurity risk to equine facilities. Known risk factors for Salmonella positivity suggest that disruptions of the gastrointestinal microflora play a key role in initiating fecal Salmonella shedding; elucidating these microbial drivers is critical to developing targeted interventions to prevent transmission of Salmonella from subclinical horses.

Hypothesis/Objectives: This study aimed to characterize the fecal taxonomic profile of horses with subclinical salmonellosis and correlate changes in Salmonella shedding status over time with shifts in the fecal microbiome.

Animals: Six adult horses from a resident herd at a veterinary teaching hospital with fecal culture-confirmed subclinical salmonellosis were included.

Methods: Samples from a prospective longitudinal study were selected for retrospective analysis. For each horse, serial Salmonella fecal cultures were performed weekly for 8 weeks. DNA was isolated from banked fecal samples (n = 48) and subjected to PCR amplification and 16S rRNA amplicon sequencing.

Results: Genus-level alpha diversity did not differ significantly over time or by Salmonella shedding status (linear mixed model ANOVA; P = 0.38, P = 0.14). Horses that resumed shedding Salmonella after ≥ 4 consecutive negative cultures (considered truly Salmonella-negative) had a simultaneous decrease in the relative abundance of Proteobacteria.

Conclusions and clinical importance: While microbial diversity of the fecal microbiome does not appear to drive fecal Salmonella shedding among subclinical horses, it is possible that a decrease in Proteobacteria creates an ecological niche that allows Salmonella to proliferate.