Potent Antimicrobial Activity of Aspergillus oryzae Fermentate Against Toxigenic Strains of Clostridioides difficile

<b>Background:</b><i>Clostridioides difficile</i> infection (CDI) remains a significant public health challenge in the United States, with limited treatment options currently available. <b>Objectives:</b> This study investigated the antimicrobial efficacy of a fungal-based fermentate derived from <i>Aspergillus oryzae</i>, cultivated in a proprietary food-grade medium, against toxigenic strains of <i>C. difficile</i>. <b>Methods and Results</b>: The ethyl acetate extract of <i>A. oryzae</i> fermentate (fungal extract) exhibited potent bactericidal activity, producing a significant zone of inhibition across all tested <i>C. difficile</i> strains, including hypervirulent Ribotype 027. Notably, 80% of the tested strains (four out of five) exhibited greater susceptibility to the fungal extract than to 5 µg vancomycin discs. Inner colony formation within the zone of inhibition was observed for all strains treated with vancomycin but only one strain was exposed to fungal extract. Time kill assays further confirmed the rapid bactericidal effect of the fungal extract, achieving complete <i>C. difficile</i> eradication within six hours. Mechanistic studies using scanning electron microscopy (SEM) and flow cytometry revealed that the fungal extract induced severe membrane disruption, leading to intracellular leakage and complete lysis. Flow cytometry analysis confirmed membrane depolarization and permeability loss on <i>C. difficile</i> cells. <b>Conclusions:</b> These findings highlight that the fungal extract of <i>A. oryzae</i> exhibits a promising antimicrobial activity against <i>C. difficile</i>. Future studies will focus on identifying its active components, evaluating its efficacy in vivo, and assessing its impact on gut microbiota to establish its potential clinical application in managing CDI.