Antibacterial and antibiofilm activities of lactonic sophorolipids against select halophilic bacteria and reference bacterial strains

Authors: BERBER, DIDEM - Maltepe University; Ashby, Richard; TOKSOZ, ORCUN - Marmara University; BIRBIR, MERAL - Marmara University; Msanne, Joseph; YILMAZ, PINAR - Marmara University; SESAL, CENK - Marmara University; VENTOSA, ANTONIO - University Of Sevilla; YALCIN, DILEK - Marmara University

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sophorolipids (SLs) are natural antimicrobials that are known for their low environmental impact, and can be employed in multiple industry and food sectors. Given the potential economic loss caused by harmful salt-tolerant bacteria affecting animal hides and leather products, SLs may be considered as effective antibacterial and antibiofilm compounds that can be used in the leather industry. In this study, the antibacterial and antibiofilm effects of SLs synthesized using different fatty acid substrates were determined against microbes commonly isolated from leather products including both moderately and slightly salt-tolerant bacterial isolates. Results confirmed that various SL classes were effective in inhibiting bacterial growth and biofilm formation with differential inhibition rates, depending on the concentrations tested. Moreover, since two of the tested strains (Bacillus tequilensis and Bacillus kochii) were previously isolated from food samples, SL applications also have potential in the food industry and can be used to control foodborne pathogens.

Technical Abstract: Sophorolipids (SLs) are glycolipid biosurfactants with potent antimicrobial activities. In the present study, the antibacterial and antibiofilm activities of three different SL mixtures produced by microbial fermentation, using oleic acid (SL-o), palmitic acid (SL-p), and stearic acid (SL-s) substrates, were tested against moderately halophilic bacteria Bacillus tequilensis ATY2, Salinivibrio costicola GA5, and Gracilibacillus dipsosauri GK1, slightly halophilic bacteria Bacillus aerius SaShS7a and Bacillus kochii SaShS9a, as well as reference bacterial strain Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922. SL-o, SL-p, and SL-s were more effective in inhibiting the growth of S. aureus (over 90% inhibition) compared to E. coli (lower than 45%). Three SL mixtures exhibited strong antibacterial activity against all tested halophilic isolates particularly at a concentration of 125 µg/mL, where inhibition exceeded 80%. The high antibacterial activity was also observed at the concentration of 62.5 µg/mL against B. tequilensis, G. dipsosauri, B. aerius, and B. kochii with over 75% inhibition, depending on the type of SL mixture. The results of the antibiofilm experiments showed very low antibiofilm activity (36%) of SL-s against E. coli at 125 µg/mL, whereas higher biofilm inhibition of E. coli was detected for SL-p and SL-o treatments at 125 and 62.5 µg/mL, respectively. The antibiofilm activity of three SLs varied depending on the test isolates. The biofilm forms of S. costicola, G. dipsosauri, and B. aerius were significantly inhibited by SL-o at the concentration of 62.5 µg/mL with high inhibition rates (84-84.5%), whereas the efficacies of SL-p and SL-s were 82% and 58%, respectively. These results demonstrate that SLs are potent antibacterial and antibiofilm agents against Gram-positive and Gram-negative bacteria, with varying efficacy in terms of antibiofilm effect depending on the SL mixture.