A bacterial sensory system that activates resistance to innate immune defenses: potential targets for antimicrobial therapeutics.

Bacteria posses multiple two component regulatory systems consisting typically of a kinase and a transcription factor that, in concert, monitor the concentrations of particular extracellular factors and regulate specific gene expression accordingly. Salmonella possess PhoP-PhoQ, which are activated under conditions of suboptimal [Mg(2+)] and result in gene expression leading to greater stability of the outer membrane. New research identifies PhoQ as a receptor for sublethal concentrations of antimicrobial peptides (AMPs), adapting bacteria for survival. The development of AMPs that do not activate Phop-PhoQ, however, should proceed with great caution: AMPs are part of the host innate immune response and bacterial resistance to newly developed AMPs could possibly lead to intractable infection in immunocompetent hosts.