Isolation, identification, and antibacterial activity of endophytic fungus from Acanthus ilicifolius

Antimicrobial-resistant bacteria pose serious public health risks, necessitating bioprospecting for novel antimicrobial drugs. The endophytic fungi of the mangrove ecosystem are hotspots for discovering new bioactive chemical compounds. In this context, an investigation was designed to determine the isolation of the major endophytic fungi inhabiting the leaves of Acanthus ilicifolius, a mangrove plant with a long history of traditional use in the Chinese and Indian medical systems. Based on the morphological characterizations and molecular analysis of internal transcribed spacer rDNA sequence data, the study identified three unique endophytic fungal species, namely, Periconia macrospinosa, Coprinopsis cinerea, and Alternaria sp. Of these, P. macrospinosa was identified as the most dominant one, with the highest relative frequency (35.22%). The antibacterial activity of P. macrospinosa isolate (CMFRI/fPM-01) was evaluated by the well and diffusion method against six human pathogens, viz., Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus. The results demonstrated a high and wide spectrum of antimicrobial action of the isolate against all the tested human pathogens, with no significant difference (P > 0.05) in the activity between the pathogens. The antibacterial activity was further confirmed by determining the fungal culture supernatant's minimum inhibitory concentration and minimum bactericidal concentration. Although the studied fungi are known from other sources, this is the first report of P. macrospinosa and C. cinerea as endophytes in A. ilicifolius leaves. The outcomes also showed that the P. macrospinosa isolate could be used to discover effective antibacterial drugs against various human diseases.