The presence of acylated homoserine lactones and diffusible signal factor in bronchoalveolar lavage fluid from horses with clinical exacerbation of severe equine asthma

Several bacteria associated with chronic lung pathology use quorum sensing (QS) signaling molecules to regulate their virulence in pure cultures and poly-microbial communities. Their excessive growth and biofilm formation in the respiratory tract increase the morbidity and mortality of inflammatory airway diseases in humans, such as chronic obstructive pulmonary disease (COPD), asthma and cystic fibrosis (CF). In horses, severe equine asthma (SEA) has many parallels to these human diseases. We hypothesized that QS molecules associated with the most common biofilm-forming lung pathogens in humans (Pseudomonas aeruginosa, Stenotrophomonas maltophilia) may also be present in the lungs of horses with SEA. Samples of bronchoalveolar lavage fluid (BALf) were taken from twenty horses with exacerbated SEA. Microbiological cultures of the BALf samples were performed. Liquid chromatography coupled with tandem mass spectrometry was used to identify C4-HSL, C6-HSL, 3-oxo-C12-HSL and 11-methyl-2-dodecenoic acid, which are associated with the QS mechanisms of Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Stenotrophomonas maltophilia was identified in three horses. Pseudomonas aeruginosa was not identified in any sample. The quorum sensing molecules C4-HSL, C6-HSL, 3-oxo-C12-HSL associated with biofilm formation by P. aeruginosa and 11-methyl-2-dodecenoic acid associated with biofilm formation by S. maltophila were not detected. It is unlikely that biofilm-forming bacterial strains associated with chronic lung disease in humans express similar virulence in SEA.