Antagonists of bacitracin.

Three groups of substances were identified which inhibit the bactericidal activity of bacitracin. Beside two divalent metals, Mg2+ and Ca2+, and a metabolite with chelating properties, citrate, the most pronounced effect was observed with pyrophosphate. Metals probably prevent access of bacitracin to the lipid carrier whereas metabolites with chelating properties deprive the bacitracin of a metal ion needed for its binding to the lipid carrier. Pyrophosphate, effective as an antagonist at very low concentrations, may intercept the binding of bacitracin to the pyrophosphate part of the target molecule.