Friend or foe? Antimicrobial peptides trigger pathogen virulence

In an age of antibiotic-resistant pathogens, antimicrobial peptides have emerged as novel therapeutics hailed for their bactericidal and immunomodulatory properties. However, a recent paper by Bader et al. demonstrates that these molecules also trigger bacteria to arm themselves against host immune responses. The authors show that the two-component regulatory system PhoP–PhoQ of Salmonella is activated not only in cation-deficient environments as previously thought, but also by binding to antimicrobial peptides, thus promoting gene transcription necessary for Salmonella survival within the host. Thus, the antimicrobial peptide might be a double-edged sword, promoting antibacterial immunity while simultaneously triggering pathogen virulence.