Single-cell, real-time detection of oxidative stress induced in Escherichia coli by the antimicrobial peptide CM15

Significance Antimicrobial peptides (AMPs) help to kill invading bacteria on skin and lung surfaces. We are developing fluorescence microscopy assays that reveal the mechanisms of action of AMPs in real time. It is increasingly clear AMP damage to bacterial cells goes far beyond permeabilization of membranes. Here we demonstrate that for Escherichia coli in aerobic conditions, the peptide CM15 [combining residues 1–7 of cecropin A (from moth) with residues 2–9 of melittin (bee venom)], induces a burst of biochemically harmful reactive oxygen species within 30 s of membrane permeabilization. In anaerobic conditions, CM15 is 20-fold less potent. AMP efficacy in vivo may be tuned to the local level of oxygenation.