Elevated concentrations of polymyxin B elicit a biofilm-specific resistance mechanism inVibrio cholerae

Abstract

Vibrio cholerae can form biofilms both in the aquatic environment and in the human intestine, facilitating the release of hyper-infectious aggregates. Due to the increasing antibiotic resistance that impedes the treatment of infections, alternatives need to be found. One of these alternatives is antimicrobial peptides, including polymyxin B (PmB), which is already used to treat infections caused by antibiotic-resistant bacteria. In this study, we first investigated the resistance of V. cholerae O1 El Tor strain A1552 to various antimicrobials under aerobic and anaerobic conditions. Increased resistance to PmB is observed in anaerobiosis, with a 3-fold increase in the dose required for 50% growth inhibition. We then studied the impact of the PmB on the formation and degradation of V. cholerae biofilms to PmB. Our results show that PmB affects more efficiently biofilm formation under anaerobic conditions. On the other hand, performed biofilms are susceptible to degradation by PmB at concentrations close to the minimum inhibitory concentration (MIC), resulting in approximately 50% reduction of the biomass. At higher concentrations, we observed less degradation and opacification of the biofilm structures within 20 minutes post-treatment, suggesting densification of the structure. This densification does not seem to result from the overexpression of matrix genes but rather from the release of DNA through cellular lysis, forming a protective shield that limits the penetration of the PmB into the biofilm.