The microflora of the lower respiratory tract of the horse: an autopsy study.

This research investigates the presence of bacteria in the lower respiratory tract of horses, and the relationship between the discovered bacteria and inflammation in the lungs. It concludes that the lower respiratory tract of horses is typically sterile or contains a small number of low pathogenic bacteria.

Study Participants and Procedure

• This autopsy study included a set of 31 thoroughbreds and 18 non-thoroughbreds.
• The aim was to identify any bacteria present in the lower respiratory tract, as well as to ascertain their significance through correlation with respective lung histological changes – microscopic examination of tissues.
• Participants were examined post-mortem at the distal trachea and seven representative sites in the lungs of each horse, by way of swabbing.

Findings

• Approximately two-thirds of the sites did not present any bacteria.
• The sites with bacteria mainly showed scant growths of coagulase negative Staphylococcus spp., E. coli, Bacillus spp., and Pseudomonas spp.
• Anaerobic bacteria (those which live without oxygen), including Clostridium perfringens, Bacteroides fragilis, and Bacteroides oralis, were only discovered on enrichment media and were recovered more often from the right lung than the left.

Comparative Analysis and Significance

• A larger species variety of bacteria were isolated from thoroughbreds than from non-thoroughbreds.
• Absense of significant inflammation in the lungs of most examined horses correlated well with the large quantity of sterile sites and the low number of found potential pathogens.
• The research indicates that the lower respiratory tract of horses is typically sterile or contains small amounts of bacteria of low pathogenicity.
• Neither Chlamydia nor respiratory viruses were isolated from any of the horses involved in the study.