The present invention pertains to compositions and methods used to ascertain if putative antibiotics trigger a cell envelope stress response in bacterial organisms. In one aspect of the invention, three two-component systems are described: LiaR & LiaS (formerly YvqCE); YvcP & YvcQ; and BceR & BceS (formerly YtsAB). These systems, for example, can be used to analyze antibiotics such as vancomycin, bacitracin, nisin, and ramoplanin, which interfere with the lipid II cycle in the cytoplasmic membrane.