Bacterial strains, media, and culture conditions

All strains isolated from human fecal samples were cultured aerobically at 37 °C for 24 h using brain heart infusion (BHI) agar. Clostridioides difficile EM304, a previously reported strain, was selected as the target strain for screening and was cultured anaerobically at 37 °C for 24 h in BHI broth⁴¹. All other Clostridioides strains for use in antimicrobial activity assays and their respective growth conditions are listed in Supplementary Table ¹. All other indicator strains used in antimicrobial activity assays and their respective growth conditions are listed in Supplementary Table ². Anaerobic conditions were maintained throughout using an anaerobic chamber (10% CO₂, 10% H₂, 80% N₂). Where solid media were required, 1.5% agar (w/v) (Oxoid, Basingstoke, UK) or 2.5% agar (w/v) was added for growth of Bacillus, and for overlay assays, 0.75% agar (w/v) was added.