Crude metabolites from endophytic fungi inhabiting Cameroonian Annona muricata inhibit the causative agents of urinary tract infections.

Urinary tract infections (UTIs) are common bacterial infections. The global emergence of multidrug-resistant uropathogens in the last decade underlines the need to search for new antibiotics with novel mechanisms of action. In this regard, exploring endophytic fungi inhabiting medicinal plants used locally against urinary tract infections could be a promising strategy for novel drug discovery. This study investigates crude metabolites from endophytic fungi isolated from Annona muricata as potential sources of antibiotic drugs to fight against uropathogens and reduce related oxidative stress. Crude ethyl acetate extracts from 41 different endophytic fungi were screened against three bacterial strains using the broth microdilution method, and fungi producing active crude extracts were identified using ITS1-5.8S rRNA-ITS2 nucleotide sequences. The antibacterial modes of action of the five most active extracts were evaluated using Staphylococcus aureus ATCC 43300 and Klebsiella oxytoca strains. The DPPH and FRAP assays were used to investigate their antioxidant activity, and their cytotoxicity against the Vero cell line was evaluated using the MTT assay. Out of the 41 crude extracts tested, 17 were active with minimum inhibitory concentrations (MICs) ranging from 3.125 µg/mL to 100 µg/mL and were not cytotoxic against Vero cell lines with a cytotoxic concentration 50 (CC50) >100 µg/mL. The more potent extracts (from Fusarium waltergamsii AMtw3, Aspergillus sp. AMtf15, Penicillium citrinum AMf6, Curvularia sp. AMf4, and Talaromyces annesophieae AMsb23) significantly inhibited bacterial catalase activity, lysed bacterial cells, increased outer membrane permeability, and inhibited biofilm formation, and the time-kill kinetic assay revealed concentration-dependent bactericidal activity. All seventeen extracts showed weak ferric iron-reducing power (1.06 to 12.37 µg equivalent NH2OH/g of extract). In comparison, seven extracts exhibited DPPH free radical scavenging activity, with RSA50 ranging from 146.05 to 799.75 µg/mL. The molecular identification of the seventeen active fungi revealed that they belong to six distinct genera, including Aspergillus, Curvularia, Fusarium, Meyerozyma, Penicillium, and Talaromyces. This investigation demonstrated that fungal endophytes from Cameroonian Annona muricata, a medicinal plant used locally to treat bacterial infections, might contain potent antibacterial metabolites with multiple modes of action. The antibacterial-guided fractionation of these active extracts is currently ongoing to purify and characterise potential antibacterial active ingredients.

Serial Exhaustive Extraction Revealed Antimicrobial and Antioxidant Properties of Platycerium stemaria (Beauv) Desv.

Microbial infections are increasing worldwide, and the widespread emergence of antibiotic-resistant pathogens poses a severe threat to public health. Medicinal plants are well-known sources of bioactive ingredients. This study was designed to determine the antimicrobial and antioxidant activities of extracts from Platycerium stemaria. The serial exhaustive extraction method using a solvent of increasing polarity from nonpolar (hexane) to polar (water) was designed to prepare crude extracts; liquid-liquid partition was used to fractionate of active extracts. The extracts and fractions were screened for antimicrobial activity on bacteria and yeasts using the microdilution method. The antioxidant activity was done using DPPH and FRAP assays. Out of the sixteen extracts screened, four (PsHex, PsH2O(H), PsMeOH(EA), and PsMeOH) exhibited potency with minimal inhibitory concentration (MIC) values ranging from 31.25 to 500 µg/mL. Out of the four extracts, two, including PsMeOH and PsMeOH(EA), exhibited DPPH radical scavenging activity with the antiradical power of 8.94 × 10-5 and 47.96 × 10-5, respectively, and ferric reducing antioxidant power values ranging from 0.34 to 61.53 µg equivalent Vit C/g of extract. The phytochemical screening of the promising crude extracts revealed flavonoids, glycosides, phenols, tannins, terpenoids, saponins, and anthraquinones. This study reports the antimicrobial and antioxidant activities of P. stemaria for the first time. The results showed that the serial exhaustive extraction approach used in this study allowed capturing the antimicrobial and antioxidant metabolites beyond the single extraction, indicating the need for a rigorous choice of an appropriate solvent and method for extracting P. stemaria. Further investigation is needed to characterize the active ingredients present in the promising extracts.