Quantitative assessment of specific bacterial taxa of the intestinal microbiota of healthy and diarrheic horses.

Overview

• This study used quantitative PCR to identify specific bacteria in the intestines of healthy and diarrheic horses, aiming to find bacterial markers that signal intestinal health or disruption (dysbiosis).

Background and Objective

• Previous research using DNA sequencing has shown that the intestinal microbiota composition differs between healthy horses and those with acute colitis (intestinal inflammation and diarrhea).
• However, changes in specific bacterial populations can provide a more direct and quantitative measure of intestinal health or dysbiosis.
• The objective was to identify which bacterial taxa differ between healthy horses and those with various forms of colitis using quantitative PCR (qPCR), a sensitive and targeted method to measure bacterial DNA abundance.

Methods

• Study Design: Retrospective multicenter cross-sectional study analyzing fecal samples collected from horses.
• Subjects:
  • 30 horses with undifferentiated colitis (unknown cause)
  • 13 horses with colitis linked to Salmonella species
  • 14 horses with antibiotic-associated diarrhea (AAD)
  • 52 healthy control horses from Canada
  • 48 healthy control horses from the United States
• Assays: Developed qPCR assays for 14 bacterial taxa relevant to gut health and dysbiosis.
• Statistical Analysis: Compared absolute abundances of bacterial taxa using appropriate tests including Welch t-test, ANOVA, Kruskal-Wallis, or Welch’s ANOVA depending on data distribution.

Key Findings

• Out of the 14 bacterial taxa tested, 7 showed significant differences in abundance between healthy and diarrheic horses.
• Common changes observed across all colitis groups included:
  • Increased abundance of Enterobacteriaceae: This bacterial family was significantly higher in all diarrhea groups compared to healthy controls. The measured log10 DNA values indicate a clear rise, for example, Canadian controls averaged 2.51 vs. 3.43 in undifferentiated colitis, showing notable bacterial expansion.
  • Increased abundance of Escherichia coli: E. coli counts were also significantly elevated in diarrheic horses across all groups, suggesting overgrowth associated with disease.
  • Decreased abundance of Turicibacter spp.: This presumably beneficial or commensal bacterial genus showed reduced levels in all colitis phenotypes, indicating its loss may correlate with intestinal dysbiosis.

Interpretation and Conclusions

• The study highlights that specific bacterial taxa are consistently altered in horses suffering from different types of colitis compared to healthy horses.
• Particularly, increased Enterobacteriaceae and E. coli combined with decreased Turicibacter spp. can serve as microbial markers of intestinal dysbiosis in horses.
• Using targeted qPCR offers a faster and cost-effective method to detect these microbial imbalances compared to broad DNA sequencing approaches.
• This quantitative approach could help veterinarians quickly identify intestinal microbiota disruption in horses, potentially guiding treatment and management of diarrheal disease.

Significance

• Improves understanding of microbial changes in equine colitis, a condition with significant health and economic impacts.
• Provides practical diagnostic tools for monitoring gut health in horses.
• May lead to better-targeted therapeutic strategies by identifying specific bacterial taxa associated with disease or health states.