Singlet excited oxygen as a mediator of the antibacterial action of leukocytes.

Human polymorphonuclear leukocytes kill a colorless mutant strain of Sarcina lutea much more readily than a carotenoid-containing strain. A similar protective effect has been reported in the organism during photodynamic inactivation, where it is attributable to the quenchintg of singlet excited oxygen by carotenoids. The findings with leukocytes support the suggestion that singlet excited oxygen acts as one of the mediators of their bactericidal action.