Biofilm Induced Tolerance towards Antimicrobial Peptides

Abstract

Increased tolerance to antimicrobial agents is thought to be an important feature of microbes growing in biofilms. We address the question of how biofilm organization affects antibiotic susceptibility. We established Escherichia coli biofilms with differential structural organization due to the presence of IncF plasmids expressing altered forms of the transfer pili in two different biofilm model systems. The mature biofilms were subsequently treated with two antibiotics with different molecular targets, the peptide antibiotic colistin and the fluoroquinolone ciprofloxacin. The dynamics of microbial killing were monitored by viable count determination, and confocal laser microscopy. Strains forming structurally organized biofilms show an increased bacterial survival when challenged with colistin, compared to strains forming unstructured biofilms. The increased survival is due to genetically regulated tolerant subpopulation formation and not caused by a general biofilm property. No significant difference in survival was detected when the strains were challenged with ciprofloxacin. Our data show that biofilm formation confers increased colistin tolerance to cells within the biofilm structure, but the protection is conditional being dependent on the structural organization of the biofilm, and the induction of specific tolerance mechanisms.

Real-Time Solvent Tolerance Analysis ofPseudomonassp. Strain VLB120ΔC Catalytic Biofilms

“…Pseudomonas aeruginosa biofilms showed a reduced susceptibility when challenged with the antimicrobial agent colistin, and it was suggested that the enhanced resistance is due to the development of a tolerant subpopulation in the biofilm. The resistance mechanisms also were linked to the adaptation or activation of a surviving phenotype, targeting physiological mechanisms, and mutations (3,9,29). Kubota and coworkers reported the increased resistance of Lactobacillus plantarum JCM 1149 biofilms to organic acids and concluded that biofilms are protected by extracellular polymeric secretions, and the three-dimensional structure of the biofilm then protects the cells inside the biofilm matrix.…”

“…Numerous studies have reported that bacterial cells in biofilms or cells artificially entrapped in a matrix are more resistant to environmental stresses (e.g., antimicrobial substances, heavy metals, toxic chemicals, organic acids, etc.) than their planktonic or freely swimming counterparts (7,9,16,19,29,40). There has been growing interest in recent years in the exploitation of these robust catalysts for biotechnological applications (e.g., biotransformations) to produce value-added chemicals (10,11,12,27).…”

New trends in peptide-based anti-biofilm strategies: a review of recent achievements and bioinformatic approaches

“…For instance, the increased survival of E. coli biofilms when treated with colistin is not related directly with biofilm forming ability, but rather to the organization of the biofilm (Folkesson et al 2008). Also, there is some evidence that biofilm formation in E. coli induces tolerance to AMPs due to changes in intra-biofilm physiochemical gradients (Folkesson et al 2008).…”

Effects of Trp- and Arg-Containing Antimicrobial-Peptide Structure on Inhibition of Escherichia coli Planktonic Growth and Biofilm Formation

“…Biofilms can tolerate up to 1,000 times more antibiotics and disinfectants than their planktonic counterparts (2,7,8). For example, Folkesson et al (12) reported that biofilm formation of E. coli K-12 increases its tolerance to polymyxin E, a polypeptide antibiotic that kills Gram-negative bacteria by disrupting membranes (34,40). Since biofilms are involved in 80% of human bacterial infections (1), it is necessary to study biofilm inhibition and dispersion by AMPs.…”