Anti-MRSA Activity and LC-HRMS Chemical Profiling of a Bioactive Fraction from the Endolichenic Fungus Pestalotiopsis lushanensis: Exploratory Network Analysis and Molecular Docking

Methicillin-resistant Staphylococcus aureus (MRSA) is an important drug-resistant pathogen, which highlights the necessity of exploring antibacterial active substances from culturable microbial resources. In this study, an endophytic fungus HF-080 was isolated from lichen Hypogymnia flavida and identified as Pestalotiopsis lushanensis. The anti-MRSA activity, chemical characteristics and candidate proteins were evaluated by rice solid-state fermentation, bioactivity-guided fractionation, antibacterial activity determination, LC-HR-ESI-MS chemical spectrum analysis, protein–protein interaction network analysis and molecular docking. Fraction 11-25-1 showed preliminary anti-MRSA activity, with a TTC-based inhibitory endpoint of 1 mg/mL and no detectable colonies upon subculture at 4 mg/mL under the tested conditions. LC-HR-ESI-MS analysis enabled the tentative annotation of 83 chemical features. However, in the absence of appropriate culture medium blanks and analytical blanks, not all detected signals could be unambiguously attributed to fungal metabolism. Network analysis preferentially screened FtsZ, RpoB, RecA and MetG, and the drug resistance-related protein PBP2a was used as an additional molecular docking target. Among the presumptive annotation candidates evaluated, Roridin A showed better computational ranking in multiple protein models. In summary, component 11-25-1 showed anti-MRSA activity in vitro, providing a basis for the separation and structural confirmation of subsequent active components and the experimental verification of candidate targets.