Light-activated porphyrin-based formulations to inactivate bacterial spores

Aim: The objective of this study was to develop porphyrin-based formulations to inactivate Bacillus spores. We probed the effect of porphyrins alone and in combination with germinants against both Bacillus cereus and Bacillus anthracis spores in the presence of light. Methods and Results: We tested the effect of two different porphyrins, amine-modified protoporphyrin IX (PPIX) and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP). Treatment with the porphyrins alone did not significantly influence spore viability. However, when spores were pretreated with a solution containing the germinants, l-alanine and inosine, the spore viability dropped by as much as 4·5 logs in the presence of light. The extent of inactivation depended on the germination conditions and the type of porphyrin used, with TMP being more effective. Conclusion: Porphyrins can be used effectively in combination with germinants to inactivate Bacillus spores. Significance and Impact of the Study: The results of this study provide evidence that porphyrins can be used to inactivate Bacillus spores in the presence of germinants and light irradiation. This finding may be general and may be extended to spores of other pathogens.