Metabolites of Endophytic Fungus Isolated from Stevia rebaudiana as Inhibitors of β-lactamase Multidrug Resistant Staphylococcus aureus

Abstract

The rise of multidrug-resistant (MDR) bacteria, particularly Staphylococcus aureus, has created an urgent need for new antimicrobial compounds capable of overcoming β-lactamase-mediated resistance. This study investigated the metabolites of endophytic fungi isolated from Stevia rebaudiana as potential inhibitors of β-lactamase-producing S. aureus. Four fungal isolates namely: Fusarium proliferatum, Colletotrichum gloeosporioides, Perenniporia tephropora, and Diaporthe siamensis, were recovered from S. rebaudiana and identified molecularly through ITS sequencing. Secondary metabolites extracted from the fungal cultures were tested against MDR S. aureus isolates obtained from contaminated farmland soils in Ogbomoso, Nigeria. Antimicrobial susceptibility testing revealed potent antibacterial activity with inhibition zones ranging from 20 to 30 mm. Chemical analysis via FTIR and GC–MS confirmed a diverse metabolic profile, identifying ten major bioactive compounds, notably oleic acid, linoleic acid, ergosterol, and β-sitosterol. In silico molecular docking against β-lactamase PDB ID: 1GHM) demonstrated significant binding affinities (up to -7.6 kcal/mol for these key metabolites. These findings establish the endophytic fungi of S. rebaudiana as a novel and promising source of metabolites with combined antimicrobial and predicted β-lactamase inhibitory potential, offering valuable leads for next-generation antimicrobial drug discovery.