Preparation of MEL-D via hydrolysis of crude MELs and their potential application in antibacterial through multimodal mechanisms

This study developed a novel strategy to prepare deacetylated mannosylerythritol lipids (MEL-D), which can disrupt cell membranes, from fermented MELs to address the challenge of inhibiting drug-resistant bacteria. Approximately 45 % of MEL-D with a purity exceeding 98 % can be obtained through acid hydrolysis of crude MELs and an integrated separation and purification process. The resulting MEL-D exhibited superior antibacterial activities compared to crude MELs against Bacillus cereus and Bacillus subtilis, with minimum inhibitory concentrations (MIC) ranging from 32 to 64 mg/L. This effective antibacterial action arises from its ability to disrupt cell membranes and biofilms. However, MEL-D demonstrated weaker antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), with an MIC as high as 512 mg/L. When combined with antibiotics, MEL-D significantly enhanced antibacterial activity and reduced the required dosage, exhibiting strong synergy with conventional antibiotics, as evidenced by FICI values in the range of 0.25–0.5. Moreover, this strategy demonstrates a favorable synergy profile when combined with antibiotics, which significantly mitigates the cytotoxicity associated with MEL-D monotherapy.