Biofilm structure as a key factor in antibiotic tolerance: insights from Bacillus subtilis model systems

Tolerance to antimicrobial agents in mature and structured biofilms presents a significant challenge in clinical and industrial applications. The contribution of biofilm physical structure to antimicrobial tolerance remains particularly poorly understood, primarily due to the lack of biofilm structure quantification and manipulation studies. To fill the gap in our knowledge, we have investigated how mechanical and biochemical disruptions of biofilm integrity affect Bacillus subtilis tolerance to antimicrobial agents. Our findings reveal that biofilm structural integrity is a major determinant of tolerance to membrane disrupting antibiotic daptomycin. Biofilm viscoelastic properties as well as antimicrobial tolerance to daptomycin were directly related to the presence of exopolysaccharide EpsA-O. In the absence of EpsA-O bacteria produced weak biofilms with markedly reduced elastic and viscous moduli that correlated with a 3-log reduction in bacterial survival rate when challenged with daptomycin. These findings underscore the protective role of biofilm structure against antibiotics and suggest that targeting biofilm structural integrity could substantially enhance antimicrobial treatment strategies for biofilm-related infections.