Potent antibacterial activity from bioactive metabolites of Colletotrichum sp. strain USS33

Fungal secondary metabolites are a rich source of bioactive compounds with potential pharmaceutical applications, including antimicrobial agents against multidrug-resistant pathogens. In this study, crude extracts of Colletotrichum sp. strain USS33, cultured in yeast malt broth, were evaluated for antibacterial activity against a panel of Gram-positive and Gram-negative bacteria, including methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA and VRSA). The extracts exhibited broad-spectrum activity, with the strongest effects observed against Pseudomonas fluorescens (23.00 ± 0.23 mm), S . aureus TISTR 1466 (22.00 ± 0.27 mm), and MRSA strain CRP45 (21.50 ± 0.87 mm). Bioautography-guided fractionation revealed that a CH 2 Cl 2 :ethyl acetate (1:1) system effectively separated the active fraction, which retained antibacterial activity against S. aureus , MRSA, and VRSA. GC–MS analysis identified benzeneethanol (11.34%) and long-chain alkenes (1-tetradecene, 1-hexadecene, and 1-octadecene) as major constituents, suggesting that both individual compounds and possible combined effects may contribute to the observed activity. These results highlight Colletotrichum species as a promising source of antibacterial metabolites. Further studies on purification, MIC determination, and mechanism of action are required.