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

• Published in: Journal of equine veterinary science Vol. 114; p. 103946
• Main Authors: Espíndola, Julia Pires, Machado, Gustavo, Diehl, Gustavo Nogueira, dos Santos, Lucila Carboneiro, de Vargas, Agueda Castagna, Gressler, Leticia Trevisan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-07-2022
• Subjects: Horse; Microbial population; Staphylococcus spp; Upper respiratory tract; Microbial population; Upper respiratory tract; Staphylococcus spp; Horse
• ISSN: 0737-0806; 1542-7412
• DOI: 10.1016/j.jevs.2022.103946

•The upper respiratory tract of healthy horses presented a diverse microbial population.•Gram-positive and negative were found in 82.91% and 40.29% of horses, respectively.•The most occurrent profile was Staphylococcus sp. + Gram-negative bacilli.•Pathogenic bacteria were isolated colonizing the nasal cavities of clinically healthy horses with the commensal.
Microbiological diagnosis of equine respiratory infections is essential for disease management. However, reliable diagnosis can be a challenge due to colonization of the upper respiratory tract (URT) by a diverse microbial population, and because there is a lack of studies with samples from healthy animals. Aiming to guide adequate URT culture, this work reports culturable microbial population from the URT of 1,010 apparently healthy horses from 341 farms in Southern Brazil and identifies the putative presence of pathogenic microorganisms. Nasal swabs were cultured in 5% blood agar, and the isolates were phenotypically identified to genus level. A diverse respiratory microbial population was found, mostly composed of Gram-positive bacteria, including Staphylococcus spp., Bacillus spp., Streptococcus spp. and Corynebacterium spp. The microbiological profile from the nasal cavity of 911 horses was described, with the five most common profiles being: (1) Staphylococcus sp. + Gram-negative bacilli (12.67%), (2) Staphylococcus sp. in pure culture (12.47%), (3) Staphylococcus sp. + Bacillus sp. (10.10%), (4) Gram-negative bacilli in pure culture (6.93%), and (5) Staphylococcus sp. + Bacillus sp. + Gram-negative bacilli (6.73%). Streptococcus equi equi and Rhodococcus equi were detected in 34 horses (3.37%), demonstrating the presence of pathogenic bacteria along with commensal microorganisms in apparently healthy animals. The disclosed data may guide and facilitate microbiological diagnosis of URT infection in horses. The significant presence of Gram-negative bacilli was evidenced, as well as the occurrence of relevant pathogens, such as S. equi equi and R. equi, thus helping to improve diagnosis and antimicrobial therapy.