Culturable Microbial Population From the Upper Respiratory Tract of 1,010 Clinically Healthy Horses in Southern Brazil.

The study investigates the variety of microbes residing in the upper respiratory tract of 1,010 healthy horses in Southern Brazil, aiming to improve diagnosis and treatment of equine respiratory infections.

Objective and Methodology

• The research aimed to offer insight into which microbes habitually reside in the upper respiratory tract (URT) of healthy horses, thus providing more reliable distinctions between normal and disease-causing microbial populations. This aids in accurate diagnosis and treatment of equine respiratory infections.
• Nasal swabs were collected from 1,010 apparently healthy horses from 341 different farms in Southern Brazil. The swabs were cultured in 5% blood agar, and the phenotypic characteristics of the isolates were determined.

Findings

• The URT of these horses were found to be inhabited by a diverse microbial population, primarily consisting of Gram-positive bacteria such as Staphylococcus spp., Bacillus spp., Streptococcus spp., and Corynebacterium spp.
• The research profiled the microbiota in the nasal cavity of 911 horses. The five most common profiles identified were: (1) Staphylococcus sp. + Gram-negative bacilli, (2) Staphylococcus sp. in pure culture, (3) Staphylococcus sp. + Bacillus sp., (4) Gram-negative bacilli in pure culture, and (5) Staphylococcus sp. + Bacillus sp. + Gram-negative bacilli.
• It was notable that Streptococcus equi equi and Rhodococcus equi, pathogenic bacteria, were found alongside normal, non-disease causing microorganisms in 34 of the horses. This suggests that even healthy horses can harbor potentially harmful bacteria in their respiratory tracts.

Implications

• The study aids in the understanding of the normal microbial community in the URT of horses. This can benefit veterinarians in making accurate URT infection diagnoses by distinguishing between commensal (normal) and pathogenic (disease-causing) microbes. In turn, this can lead to more targeted and effective treatment strategies.
• The presence of Gram-negative bacilli and prominent pathogens such as S. equi equi and R. equi, even in healthy horses, highlights the need for caution and thoroughness in diagnosing equine URT infections.