Isolation and Characterization of Fungal Endophytes From <i>Helichrysum oocephalum</i> , Evaluating Their Antimicrobial Activities, and Annotation of Their Metabolites

Antibiotic resistance is one of the biggest threats to global health. Fungal endophytes are important sources of active natural products with antimicrobial potential. The purpose of this study was to characterize the endophytes coexisting with Helichrysum oocephalum, evaluate their antimicrobial activities, and annotate the endophytes metabolites. Six fungal species, including Fusarium avenaceum and Fusarium tricinctum, were identified. Endophytes were cultured, and their metabolites were extracted. The antimicrobial effects of the extracts were tested against Staphylococcus aureus, Bacillus cereus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. In addition, anti-biofilm effects of the extracts were examined against P. aeruginosa and S. epidermidis. The metabolites in the most active extract were annotated on the basis of the LC-ESI-QToF-MS/MS data. In anti-biofilm studies, F. avenaceum extract was effective in destroying and inhibiting the biofilm formation of S. epidermidis. LC-MS analysis showed that most of the identified compounds in the active extracts were enniatins (cyclic hexadepsipeptides). However, apicidin derivatives were also annotated. Our results revealed that these endophytes, especially Fusarium species, have antimicrobial activity against S. aureus, B. cereus, and C. albicans and anti-biofilm activity against S. epidermidis. According to the literature, the observed antimicrobial activity can be attributed to the enniatins. However, further phytochemical and pharmacological studies are necessary in this regard.