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

Abstract

Vibrio cholerae can form biofilms in the aquatic environment and in the human intestine, facilitating the release of hyper-infectious aggregates. Due to the increasing antibiotic resistance, alternatives need to be found. One of these alternatives is antimicrobial peptides, including polymyxin B (PmB). In this study, we first investigated the resistance of V. cholerae O1 El Tor strain A1552 to various antimicrobials under aerobic and anaerobic conditions. An 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 the degradation of V. cholerae biofilms to PmB. Our results show that PmB affects more efficiently biofilm formation under anaerobic conditions. On the other hand, preformed biofilms are susceptible to degradation by PmB at concentrations close to the minimal inhibitory concentration. At higher concentrations, we observe an opacification of the biofilm structures within 20 min post-treatment, suggesting a densification of the structure. This densification does not seem to result from the overexpression of matrix genes but rather from DNA release through massive cell lysis, likely forming a protective shield that limits the penetration of the PmB into the biofilm.

Keywords: Anaerobiosis; Biofilm; DNA; Polymyxin; Resistance; Vibrio cholerae.