A pigment-producing endophytic fungus isolate, Alternaria jacinthicola, was isolated and identified from Sesbania grandiflora stems. Fourier transform infrared spectroscopy (FTIR) and ultrahigh-performance liquid chromatography (UHPLC)- mass spectrometry analysis were performed to identify the different metabolites present in the crude extract. The major compounds in the crude extract were identified and confirmed using mass spectroscopic studies. Cytotoxicity studies with brine shrimp indicated an LC 50 of the crude extract above 200 µg/mL, and an acute toxicity study with Oreochromis mossambicus fingerlings indicated an LD 50 of the crude extract above 1000 µg/Kg with mortalities observed from 600 µg/Kg. In vitro antioxidant assays, such as the 2,2-diphenyl-1-picrylhydrazyl assay, the hydrogen peroxide assay, the 2,2′-azinobis-(3-ethylenebenzothiazoline)-6-sulfonic acid assay, the total reducing power assay, and the total antioxidant capacity assay, confirmed the antioxidant properties of the crude extract. The bioactive metabolites present in the crude extract inhibited the aquatic bacterial pathogens, Aeromonas hydrophila and Vibrio parahaemolyticus . It showed maximum inhibition zones of 19.83 ± 0.16 mm ( A. hydrophila ) and 19.66 ± 0.33 mm ( V. parahaemolyticus ) at the highest concentration (500 µg/mL). Molecular docking studies with the target proteins of A. hydrophila and V. parahaemolyticus confirmed the binding efficiency of the identified metabolites (ligands). The crude extract from the endophytic fungus was used to treat the bacterial manifestations caused by these pathogens. O. mossambicus fingerlings were challenged with A. hydrophila and V. parahaemolyticus to assess clinical manifestations and mortality. The crude extract was used to treat the O. mossambicus fingerlings challenged with these aquatic pathogens. A survival rate of 77.77% of A. hydrophila and 66.66% of V. parahaemolyticus challenged O. mossambicus was observed when treated with the crude extract. Histopathological, biochemical, and antioxidant stress marker studies confirmed the potency of the crude extract in treating infections caused by A. hydrophila and V. parahaemolyticus . • A. jacinthicola crude extract was evaluated as a natural alternative to antibiotics against A. hydrophila and V. parahaemolyticus in O. mossambicus. • In vitro antioxidant and antibacterial assays confirmed the bioactive potential of the crude extract. • The extract improved fish survival rates to 77.77% against A. hydrophila and 66.66% against V. parahaemolyticus .
Vijayakumar et al. (Thu,) studied this question.