Aeromonas hydrophila induces skin disturbance through mucosal microbiota dysbiosis in Pangasianodon hypophthalmus

Bacterial pathogens are well-equipped to adhere to and initiate infection in teleost fish. The fish skin mucus serves as the first barrier against environmental pathogens. The mucus harbors commensal microbes that form the microbiota, impacting the host physiological and immunological regulation. However, how the skin mucosal microbiota responds to the presence of pathogens remains largely unexplored. Thus, little is known about the status of skin mucus prior to the infection with noticeable symptoms. In this study, we aim to investigate the interaction between pathogen and skin mucosal microbiota, as well as the fish skin immune responses in the presence of pathogens. By challenging striped catfish (Pangasianodon hypophthalmus) with different concentrations of bacterial pathogen Aeromonas hydrophila (AH), the skin immune response and the mucosal microbiota were examined by qPCR and 16S rRNA gene sequencing analysis. We found a pathogen concentration able to stimulate the skin immune response associated with the significant mucosal microbiota change and re-confirmed with the ex vivo fish skin model. Further analysis indicated that the change was attributed to the significant increase in opportunistic pathogens over AH. We concluded that the presence and increase of AH results in dysbiosis of mucosal microbiota that can stimulate skin immune response. We believe our work can shed some light on host-pathogen-commensal microbiota interaction and therefore contribute to aquaculture infection prevention. IMPORTANCEThe fish skin mucosal microbiota is essentially the first barrier in response to the presence of pathogens. This study is the first study to elucidate the interaction between the AH, the skin mucosal microbiota, and the striped catfish skin at the initiation stage of infection. Our study provides a platform to study both the correlation and causation of the interaction between pathogen, the fish skin, and the skin mucosal microbiota. This work provides information that changes in the AH-induced mucosal microbiota result in skin disturbance with immune stimulation.