Oreochromis niloticus gastrointestinal microbiota affected by the infection with Staphylococcus haemolyticus and Providencia vermicola, two emerging pathogens in fish aquaculture

The rapid intensification of tilapia aquaculture is associated with losses due to emerging pathogens. The gastrointestinal microbiota plays a vital role in the host's health by modulating the immune system and several physiological functions. Recent studies suggest that bacterial pathogens may deleteriously affect the microbiota structure. This study analyzed the effect of challenging tilapia with two emerging bacterial pathogens: Staphylococcus haemolyticus and Providencia vermicola, on the stomach and intestinal microbiota. Immediately after infection, fish started showing disease signs, tilapia infected with S. haemolyticus and P. vermicola registered 40 and 67% survival after seven days, while no mortality was reported in the control group during the trial. Amplicon libraries constructed by amplifying the V4 region of the 16S rRNA gene were analyzed. Proteobacteria was the most dominant phylum in the stomach and intestine of all infection groups. Staphylococcus haemolyticus infection disrupted both stomach and intestine microbiota. For instance, Bacteroidetes abundance increased while Proteobacteria dropped in the stomach of fish infected with S. haemolyticus. Both alpha and beta diversity indexes showed a clear differentiation of this group from the control and P. vermicola-infected fish. The microbiota of the stomach and intestine of this last group was also affected, although the effects were not as severe as in the case of the S. haemolyticus challenge. Results revealed that both emerging pathogens could lead to dysbiosis, affecting the functioning of the tilapia gut microbiota.