Bacterial isolates and antimicrobial susceptibility patterns in tracheal wash samples from horses with equine asthma in Poland.

Introduction: Equine asthma (EA) is a chronic inflammatory lower-airway disease. Bacterial growth from tracheal wash (TW) may occur in samples from horses with EA, but may represent colonisation rather than active infection. This study described cultivable bacterial isolates recovered from TW samples from horses with EA in Poland and assessed their antimicrobial susceptibility patterns and association with month/season of sampling and airway neutrophil percentage. Material and Methods: In total, 165 adult horses diagnosed with EA according to American College of Veterinary Internal Medicine-based criteria underwent endoscopy, TW sampling with a double-guarded catheter and bronchoalveolar lavage fluid cytology. The samples were cultured conventionally and their bacterial content identified with MALDI-TOF MS; bacteria were tested for antimicrobial susceptibility. Associations between culture results and categorical variables were analysed using chi-squared/Fisher-type tests with Monte Carlo simulation where appropriate; effect size was reported as Cramer's V. Results: Culture results were positive in 117/165 horses' samples (70.9%), and bacteria were isolated from 116/165 (70.3%). The most frequently recovered bacteria were Conclusion: Cultivable bacteria are frequently recovered from TW samples of horses with EA. Positive culture results should not be interpreted as evidence of bacterial infection without supporting clinical and cytological findings. Antimicrobial treatment, when clinically justified, should be guided by culture and susceptibility testing.