Sophorolipids (SLs) are bacterial glycolipid biosurfactants that are produced in relatively large yields via fermentation and possess a much better environmental footprint than petroleumbased surfactants. Sophorolipids were prepared in the presence of palmitic acid, stearic acid, and oleic acid in order to increase structural variability. Structural lactones composed greater than 90% of the SLs produced regardless of substrate. These distinct SLs were then assessed for their antimicrobial behavior against both Gram+ (Listeria) and Gram- (Escherichia coli, Salmonella enterica) bacterial strains that are commonly associated with foodborne illness. Results suggested that Gram+ bacterial strains were more susceptible to the antimicrobial action of SLs than were Gram- strains. Without the thick outer membrane, Gram+ strains are easily accessible for SLs to intercalate into the plasma membrane and disrupt normal membrane function; however, in vitro studies showed that SLs in the presence of 20% ethanol were effective in inactivating E. coli O157:H7 within 2 hours of treatment reducing the population from 7.1 log CFU/mL to a non-detectable level. Transmission Electron Microscopy (TEM) revealed that SLs caused membrane damage in E. coli by separating the outer membrane from the plasma membrane. This phenomenon caused structural damage to the membranes and improved antimicrobial action. In all cases SLs showed an ability to inhibit/kill harmful bacteria which might lead to a larger array of weapons to combat foodborne illness.

Antimicrobial character of lactonic sophorolipids against select bacterial strains commonly associated with foodborne illness

252nd National Meeting (2016)

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