Identification and Assessment of Secondary Metabolites from Three Fungal Endophytes of Solanum mauritianum Against Public Health Pathogens

Fungal endophytes, symbiotic microorganisms residing within plants, are renowned for producing bioactive secondary metabolites with diverse beneficial properties. We investigated the antimicrobial potential of fungal endophytes isolated from <i>Solanum mauritianum</i>, an invasive weed, against clinically significant bacterial pathogens. Selected fungal endophytes (<i>Penicillium chrysogenum</i>, <i>Fusarium</i> sp., and <i>Paracamarosporium leucadendri</i>) were isolated from the plant's leaves and fruits. Their crude extracts were tested against various referenced strains, such as <i>Mycobacterium</i> species (<i>M. smegmatis</i> ATCC 607 and <i>M. bovis</i> ATCC 27290), <i>Staphylococcus aureus</i> ATCC 6571, <i>Bacillus subtilis</i> ATCC 11774, <i>Klebsiella</i> species (<i>K. pneumoniae</i> ATCC 10031 and <i>K. oxytoca</i> ATCC 8724), <i>Escherichia coli</i> ATCC 10536, and <i>Pseudomonas aeruginosa</i> ATCC 10145, using the Kirby-Bauer disk diffusion method. Resazurin Microtiter Assay was used for the determination of the minimum inhibitory concentration. The chemical nature of the secondary metabolites in the crude extracts produced by fungal endophytes was evaluated using high-resolution liquid chromatography-mass spectrometry (LC-MS) using water and acetonitrile gradient. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS/MS) was employed for untargeted metabolomics. LC-QTOF-MS/MS identified 63 bioactive compounds across the three endophytes. <i>P. chrysogenum</i> had the highest activity against <i>S. aureus</i> and <i>M. smegmatis</i> (1.15 mg/mL and 0.02 mg/mL, respectively), while <i>P. leucadendri</i> demonstrated moderate activity against <i>M. smegmatis</i> (2.91 mg/mL) and <i>E. coli</i> (1.16 mg/mL). <i>Fusarium</i> sp. exhibited the broadest spectrum of antibacterial activity, with MIC values ranging from 0.03 mg/mL (<i>B. subtilis</i>) to 10 mg/mL (<i>M. smegmatis</i>). <i>P. leucadendri</i> produced 29 metabolites, <i>Fusarium</i> sp. had 23 identified metabolites, and a total of 11 metabolites were identified from <i>P. chrysogenum</i>. The fruits of the plant, accounting for 60%, appeared to be the most abundant in the endophyte diversity when compared to the stems and leaves. This study highlights the potential of fungal endophytes from <i>S. mauritianum</i> as a source of novel bioactive compounds, particularly against multidrug-resistant pathogens, contributing to the ongoing efforts to combat antimicrobial resistance.