The effect of aerosolized bacterial lysate on experimentally induced Mannheimia haemolytica pneumonia in calves.

Bacterial imbalances are observed in intestinal diseases and fecal microbiota transplantation (FMT) has been used to restore the intestinal microbiota of horses. However, there is evidence that the current methods proposed for FMT in horses have limited efficacy. The objective of this study was to concentrate the bacteria present in the donor stool by centrifugation, and to test the effect in horses with antibiotic-induced dysbiosis. One healthy 11-year-old horse was selected as a fecal donor and 9 horses were given trimethoprim sulfadiazine (TMS) for 5 days to induce dysbiosis. Horses received either a concentrated FMT (cFMT, n = 3), fresh unconcentrated FMT (fFMT, n = 3), or 10% glycerol solution (vehicle, VEH, n = 3) by nasogastric tube for 3 days. Fecal samples were collected on Days 0, 4, 9, 11, and 21 for microbiota analysis (Illumina sequencing). The TMS significantly changed the bacterial composition of horses' feces (D0 versus D4). The composition of the cFMT and fFMT recipient horses was significantly different after transplantation compared to after antibiotic-induced dysbiosis (D4 versus D11), whereas the microbiota of the vehicle recipients was not, indicating that both protocols induced transient changes. However, preparation of FMT solutions markedly changed the original composition present in the donor's feces, with significant enrichment of Escherichia genus in the cFMT. Individual susceptibility to restoration of the microbiota was observed in horses, similar to what is known for other species. Our results suggest that concentrating bacteria should not be recommended in preparation of FMT solutions and that further research is required to improve current methods recommended to perform FMT in horses.