Indole can be an important regulator of biofilm formation, although the effect of biofilm formation may be dependent on whether or not the bacterium produces indole endogenously.54 Endogenous oxidative stress increases tryptophanase activity, increases indole and delays biofilm formation.55 Consistent with our observations, decreases in indole coincides with increased biofilm formation.52 Ongoing studies will investigate the role of changes in indole concentrations on persistence of NTHI during experimental OM. The gene discussed is TDO2; the disease is ocular melanoma.