Resistance response to Arenicin derivatives in Escherichia coli.

The rising prevalence of antibiotic resistance poses the greatest health threats. Antimicrobial peptides (AMPs) are regarded as the potentially effective therapy. To avoid current crisis of antibiotic resistance, a comprehensive understanding of AMP resistance is necessary before clinical application. In this study, the development of resistance to the anti-Gram-negative bacteria peptide N6NH (21 residues, β-sheet) was characterized in E. coli ATCC25922. Three N6NH-resistant E. coli mutants with 32-fold increase in MIC were isolated by serially passaging bacterial lineages in progressively increasing concentrations of N6NH and we mainly focus on the phenotype of N6NH-resistant bacteria different from sensitive bacteria. The results showed that the resistance mechanism was attributed to synergy effect of multiple mechanisms: (i) increase biofilm formation capacity (3 ~ 4-fold); (ii) weaken the affinity of lipopolysaccharide (LPS) with N6NH (3 ~ 8-fold); and (iii) change the cell membrane permeability and potential. Interestingly, a chimeric peptide-G6, also a N6NH analog, which keep the same antibacterial activity to both wild-type and resistant clones (MIC value: 16 μg/mL), could curb N6NH-resistant mutants by stronger inhibition of biofilm formation, stronger affinity with LPS, and stronger membrane permeability and depolarization than that of N6NH.