Genotypic and phenotypic analysis of Salmonella strains associated with an outbreak of equine neonatal salmonellosis.

This study analyzed genetic and phenotypic features of Salmonella strains related to a horse neonatal disease outbreak, evaluating both their similarities and differences, with findings pointing to contaminated feed as the most likely disease source.

Research Objectives

• The research aimed at analyzing the genetic composition (genotype) and observable characteristics (phenotype) of various Salmonella choleraesuis serotype ohio (S. ohio) strains.
• These strains were associated with an outbreak of equine neonatal salmonellosis, a bacterial disease that affects young horses, on a Thoroughbred farm.
• The intention was to compare the strains recovered from the outbreak with those from different animals, feed, and environmental sources, in order to find commonalities or differences that could shed light on the outbreak’s origin.

Methods

• This analysis involved various scientific methods like biochemical profiling, antimicrobial susceptibility patterns, and plasmid profiling, which assesses the small DNA molecules within a cell that are separate from chromosomal DNA, and others.
• Ribotyping, a technique used to classify microorganisms based on differences in rRNA genes, and restriction endonuclease analysis, which identifies DNA sequences, were also used in the comparison process.
• The study analyzed 46 outbreak associated and non-outbreak associated S. ohio isolates.

Findings

• Differences in antimicrobial susceptibility patterns, phage susceptibility, and plasmid profiles distinguished outbreak isolates from other equine, bovine, porcine, and some poultry isolates.
• Feed and other poultry isolates, particularly those in close geographic proximity to the outbreak, were identical to the outbreak isolates using all employed methods.
• This analysis, in combination with on-farm investigative studies, suggested that contaminated feed was the most probable Salmonella source in this outbreak.