Effect of Bacillus subtilis on intestinal apoptosis of grass carp Ctenopharyngodon idella orally challenged with Aeromonas hydrophila

The influence of Bacillus subtilis Ch9 on intestinal apoptosis of grass carp Ctenopharyngodon idella challenged with Aeromonas hydrophila was studied. Groups of grass carp were orally intubated with B. subtilis or phosphate buffered saline for 3days and subjected to oral A. hydrophila challenge. Intestinal tissues were collected and prepared for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay, real-time quantitative polymerase chain reaction analysis of caspase-3 and -8 and b-cell lymphoma-2 protein (bcl-2), histopathological analyses and measurement of caspase-3 and -8 activities at 0, 12, 24, 48, 72 and 96h post-challenge. TUNEL analyses demonstrated that B. subtilis induced intestinal cell apoptosis, and caspase-3 and -8 activities increased significantly compared to in the control and A. hydrophila groups. The intestinal damage due to A. hydrophila was also reduced. However, messenger RNA transcript levels of caspase-3 and -8 and bcl-2 were not markedly elevated. These results suggested that B. subtilis Ch9 increased intestinal apoptosis in fish challenged with A. hydrophila, and that B. subtilis Ch9-induced caspase-dependent apoptosis may play an important role in reducing intestinal damage following A. hydrophila challenge.