Synergistic effect of lipopeptide biosurfactant with antibiotics against Escherichia coli CFT073 biofilm

Biofilms are microcolonies of microbes adherent to biotic and abiotic surfaces, often responsible for chronic infections and medical device contamination. Escherichia coli is one of the prevalent pathogens involved in uropathogenic infections and contamination of catheters. A biosurfactant produced by Bacillus licheniformis V9T14 was tested alone and in association with various antibiotics against a mature 24-h uropathogenic E. coli CFT073 biofilm. Biofilm was grown on polystyrene pegs of a Calgary Biofilm Device, providing a tool to evaluate the efficacy of antimicrobial agents. Antibiotics tested were ampicillin, cefazolin, ceftriaxone, ciprofloxacin, piperacillin, tobramycin and trimethoprim/sulfamethoxazole (19:1). Biosurfactant alone at the concentrations tested was not able to remove the adherent cells of the pre-formed biofilm. However, the difference between the effect of antibiotic alone and in combination with the biosurfactant was significant and exceeded 1 log₁₀ (90%) reduction in most cases. Results of this study indicate that V9T14 biosurfactant in association with antibiotics leads to a synergistic increase in the efficacy of antibiotics in biofilm killing, and in some combinations leads to total eradication of E. coli CFT073 biofilm.