Exhaled breath condensate in horses: a first microbiological insight

Exhaled breath condensate (EBC) is a non-invasive method for obtaining samples reflecting the airway lining fluid; however, its microbiological composition remains poorly characterized.

To perform an exploratory microbiological comparison of EBC in clinically healthy horses maintained under different environmental conditions.

An observational study included 30 mares equally distributed into two groups: horses housed in stalls (Racetrack group) and horses maintained under pasture conditions (Farm group). EBC samples were collected using a validated device developed by the research group. Prior to sampling, nasal cleaning was performed with dry gauze. Condensed droplets were recovered using sterile swabs, placed in Stuart transport medium, and submitted for blinded microbiological analysis. Samples were cultured on blood agar and MacConkey agar, followed by colony counting, Gram staining, and bacterial identification using biochemical tests.

No bacterial growth was detected in control samples from collection surfaces. Significantly more Gram-positive colonies were observed compared to Gram-negative colonies in both farm horses (4,013 ± 1,073 vs. 1,713 ± 1,349; P < 0.001) and racetrack horses (2,967 ± 555 vs. 213 ± 178; P < 0.001). A similar pattern was observed in environmental samples in both Farm (16 ± 13 vs. 0 colonies; P < 0.001) and Racetrack environments (1,220 ± 806 vs. 38 ± 9 colonies; P < 0.001).

These findings provide initial characterization of culturable bacteria recovered from equine EBC and support non-invasive collection feasibility. Differences between systems suggest that environmental and management-related factors may influence the detected profiles.