Enhanced antimicrobial and antibiofilm activity of acetylated withanolide D derived from <i>Iochroma arborescens</i>

This work investigates the antibacterial and antibiofilm properties of withanolide D (WD) from <i>Iochroma arborescens</i> and its acetylated version (WDA). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined using microdilution assays. WD showed MICs ranging from 250 to 500 µg/mL against <i>Staphylococcus aureus</i> and <i>Staphylococcus epidermidis</i>. In contrast, WDA exhibited superior potency, with MICs of 31.2 µg/mL for <i>S. aureus</i> and 15.2 µg/mL for <i>S. epidermidis</i>, and MBCs of 31.2 µg/mL for both. WDA also significantly reduced biofilm biomass and viable cell counts for both strains. Furthermore, WDA disrupted pre-formed biofilms, with notable reductions in <i>S. aureus</i> colony-forming units. Scanning electron microscopy revealed decreased cell clustering and surface damage in WDA-treated bacteria. These findings suggest that WDA is a potent antimicrobial and antibiofilm agent with potential applications against biofilm-forming pathogens.