Microbial populations vary between the upper and lower respiratory tract, but not within biogeographic regions of the lung of healthy horses.

The research article examines the diversity of microbial populations in different areas of the respiratory tract in healthy horses, showing differences between upper and lower respiratory locations, but not within different regions of the lung.

Objective and Methodology

• The study aimed to understand the variability and distribution of microbial populations across distinct locations within a horse’s respiratory tract.
• The researchers utilized samples from four healthy adult horses. Samples were obtained using nasopharyngeal lavage (NPL), transtracheal aspirate (TTA), and bronchoalveolar lavage (BAL) techniques, with six distinct regions within the lung sampled via BAL.
• The samples underwent full-length 16S ribosomal DNA sequencing and microbial profiling analysis to identify and compare the microbial populations present.

Findings

• The analysis revealed a significant diversity in the microbial populations, with over 1797 ASVs identified across all samples. This number was reduced to 94 taxa following tip agglomeration and prevalence filtering.
• Variability was observed in the number and diversity of taxa across different horses, types of samples, and BAL locations. The predominant phyla were Firmicutes, proteobacteria, and actinobacteria.

Variations Between Upper and Lower Respiratory Tract

• Significant differences were discovered in microbial richness and phylogenetic diversity between samples from NPL, TTA, and BAL, manifesting the distinct microbial populations in the upper and lower respiratory tracts.
• The type of sample (NPL, TTA, or BAL) and the specific horse from which the sample was taken contributed significantly to the Bray-Curtis compositional diversity.
• The Weighted Unifrac metric, a type of beta-diversity measure comparing community composition, was only affected by whether the sample was from the upper (NPL and TTA) or lower (BAL) respiratory tract.

No Variations Within Lung Regions

• Despite the variability between upper and lower respiratory tract, the research found no significant variation in microbial populations within different biogeographic regions of the lung – the distinct segments sampled via BAL.
• This finding indicates that bronchoalveolar lavage fluid obtained using standard clinical techniques, effectively a “blind” sample without targeting a specific lung region, can be sufficient for future studies in healthy horses.