SCN ligands potentiate the antimicrobial activity of SCN in a defined growth medium. In M63 minimal medium, supplementation with SCN ligand catechol, pyrogallol, or caffeic acid (5 μm) limits E. coli UTI89 growth when combined with 1.5 μm SCN. Treatment with 1.5 μm SCN alone (SCN + water) does not limit bacterial growth in M63 minimal medium. Growth restriction is most dramatic in the enterobactin-deficient mutant, UTI89ΔentB, which is also not inhibited by SCN alone (water condition). Cultures were grown at 37 °C for 20 h and plated for cfu enumeration; bars indicate the mean of at least four independent cultures; error bars represent S.D. *, p < 0.05; **, p < 0.01; ****, p < 0.0001; one-way analysis of variance compared with water addition control.