Photodynamic antimicrobial activity of avian eggshell pigments

Pigmentation in avian eggshells appears to be associated with shell strength, temperature regulation, and camouflage. The pigments found in eggshells are mainly porphyrins, which have been utilized therapeutically as photosensitizers. Here, we examined the photoinactivation of gram-positive (Staphylococcus aureus, Bacillus cereus) and gram-negative bacteria (Escherichia coli, Salmonella enteritidis) by hen eggshells and their pigments. The results indicated that eggshells have a light-dependent antimicrobial activity against gram-positive, but not gram-negative, bacteria. Our results indicate the possibility that the natural pigments used therapeutically have evolved in nature as a defence system.