The clinical significance of Nicoletella semolina in horses with respiratory disorders and a screening of the bacterial flora in the airways of horses

Nicoletella semolina, a member of the family Pasteurellaceae, can be isolated from the airways of horses with respiratory disorders. However, its role as a potential or opportunistic pathogen is not clear nor is its presence as part of the normal flora. We therefore investigated the presence and bacterial load of N. semolina in healthy and diseased horses. Samples from a healthy control group were compared with samples from the routine analysis of horses with a clinical history of respiratory disorders. A total of 1770 nose swabs and 1132 tracheal aspirate samples were analysed and subjected to conventional bacteriological examination.N. semolina was isolated from 12 (6%) of 207 nose samples from the healthy control group and from 42 (3%) of 1563 samples from horses with respiratory disorders. In tracheal aspirate, N. semolina was isolated from 7 (3%) of 211 samples from the control group and 49 (5%) of 921 samples from horses with respiratory disorders. Other bacteria were also isolated in laboratory analyses, the most commonly isolated bacterium in both the control group and the respiratory disorders group being Streptococcus equi subsp. zooepidemicus. It was isolated in 21% of tracheal aspirate from the control group and 33% of those from horses with respiratory disorders.In conclusion, N. semolina is not a primary pathogenic bacterium, as it was isolated at similar frequencies in horses with respiratory disorders and those in the healthy control group.