Biofilm Inhibitory Effect of a Biosurfactant

Objectives: Biofilms are highly functional, complex, and surface-adhered organization of microbial communities, encased and protected by a self-produced, protective polymeric matrix termed the extracellular polymeric substance (EPS). The microbes in biofilms are at least 1000-fold more resistant to antimicrobial agents, compared to their planktonic counterparts. Biosurfactants are FDA-approved, microorganism-produced, biodegradable, amphiphilic molecules. The most commonly studied type of biosurfactants is sophorolipid (SL), extracted from non-pathogenic yeasts. SLs are composed of lactonic and acidic components, which are responsible for antimicrobial action and detergent action respectively. We hypothesized that the crude sophorolipids comprising both lactonic and acidic forms will exhibit significant antibacterial activity and can be used to thwart biofilms of Enterococci (E. faecalis and E. faecium), key pathogens of medical relevance. The objective of this study was to investigate the effects of the SL on Enterococci (E. faecalis and E. faecium) biofilms.
Methods: Colonies of E. faecalis (OG1RF) and E. faecium (HKU568) were taken from the overnight bacterial culture. The antimicrobial effect of the unfiltered crude SL on both was investigated through determination of the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentrations (MBC). Its effect on biofilm was assessed using the crystal violet assay to determine the Minimum Biofilm Inhibitory Concentration (MBIC).
Results: The addition of crude SL to bacterial suspensions significantly decreased the cell viability of both species. MIC90 of crude SL was determined to be 250μg/mL at which it inhibits >90% bacterial growth for both the bacterial species. For MBIC values, E. faecalis required a minimum 250μg/mL and E. faecium required a minimum of 125μg/mL for 50% of biofilm formation reduction and 250μg/mL for 90% of biofilm inhibition.
Conclusions: In conclusion, the results obtained from this study suggest that sophorolipid biosurfactant displays significant antibiofilm effects on both E. faecalis and E. faecium.