Antimicrobial effects of purified sophorolipids congeners on pathogenic skin bacteria

The majority of pathogens associated with skin infections have developed resistance to antibiotics due to their overuse, hence, the need for novel and more effective antimicrobial agents. The antimicrobial effects of microbial sophorolipids have been demonstrated in several studies; however, most of these studies utilized crude mixtures and poorly characterized preparations of sophorolipids resulting in significant inter-study variations, which are difficult to interpret. Therefore, to broaden the potential applications of sophorolipids and make them attractive for use as effective antimicrobial agents, the antimicrobial effects of highly purified and properly characterized congeners of sophorolipids were assessed on Cutibacterium acnes, Staphylococcus aureus, and Streptococcus pyogenes in comparison with synthetic sodium lauryl ether sulphate (SLES). The viability of bacterial cells was determined using broth dilution and MTT assays while cell morphology was examined using Live/Dead Baclight staining assays. Analysis of cell viability showed that while 60 μg mL-1 of Lactonic sophorolipids (LSL) significantly reduced cell viability of all bacterial strains (p ≤ 0.001), Acidic sophorolipids (ASL) and SLES had no significant effects on the bacterial cells. Moreover, Live/Dead Baclight staining assays revealed a drastic reduction in cell population in LSL treatment groups, which was absent in ASL and SLES treatment groups. These results demonstrate that the antimicrobial effects of purified sophorolipids congeners differ depending on their chemical structure. Furthermore, LSL could as antimicrobial agents, be effective in “fighting” C. acnes, S. aureus, and S. pyogenes, which are the leading cause of acne vulgaris, atopic dermatitis, and impetigo, respectively.