DIFFERENTIAL INACTIVATION OF SURROGATE VIRUSES WITH MEROCYANINE-540

Bacteriophages may be useful as surrogates for animal viruses when the virucidal properties of different photosensitizing compounds are initially investigated. We studied photoinactivation of four bacteriophages, phi-X174, T7, PRD1, and phi-6, by the dye merocyanine 540 (MC540) (15-mu-g/mL). Merocyanine 540 (MC540) should be most effective with lipid-containing viruses, since it is primarily lipophilic (but also binds to proteins). Two of the phages, PRD1 and phi-6 contain lipid, with only phi-6 having an external lipoprotein envelope. Filtered radiation (450-600 nm) from a 750 W projector was used at 16-100 W/m2. The survival curves of the different viruses clearly demonstrated different levels of sensitivity to photoinactivation by MC540, with phi-6 (D(o) = 1.5 kJ/M2) being the most sensitive, followed by T7 (21-fold less sensitive). While both PRD1 and phi-6 have lipid components, only phi-6 was photoinactivated by MC540. Thus the internal lipid components of PRD1 were not sufficient to allow photoinactivation by this dye, at fluences up to 300 kJ/m2. For comparison, we also photoinactivated Herpes simplex virus (D(o) = 0.053 kJ/m2) and found it to be 28-fold more sensitive than phi-6 to photoinactivation by the same concentration of MC540. Thus phi-6 may be used as a surrogate for enveloped human viruses for photoinactivation by lipophilic dyes, but the results may only be useful qualitatively.