Congo red, but not related azo dyes, inhibits LtaS in vitro and against WTA-deficient S. aureus strains. (A) 1 inhibits in vitro LTA polymerization in proteoliposomes in a dose-dependent manner. (B) Structures of azo dyes tested against S. aureus strains and proteoliposomes. (C) Replicate dot blots of assays containing the indicated concentrations of 1 and 2 (for 3, 4, and 1771, see Figure S8). (D) 1 selectively inhibited the growth of a Newman ΔtarO strain, but not Newman (Figure S9).