Comparative kinetics of hematoporphyrin derivative uptake and susceptibility of Bacillus subtilis and Streptococcus faecalis to photodynamic action.

Hematoporphyrin derivative (HpD) is widely used in photoradiation therapy of tumors and other diseases, and has been shown to affect the viability of gram positive bacteria. This investigation assessed the efficiency of binding of HpD to Bacillus subtilis and Streptococcus faecalis when HpD-treated organisms were exposed to red light. Kinetic studies indicated that the amount of HpD bound increased with increasing external concentration of HpD until saturation of binding sites was reached. S. faecalis had a higher affinity for HpD and was more susceptible to photoinactivation than B. subtilis. The data from this study suggest that differences in susceptibility of microorganisms to photoinactivation are directly related to the affinity of each strain for HpD.