Multiplicity Reactivation of Human Cytomegalovirus Inactivated by Ultra-violet Light

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Abstract
The sensitivity to inactivation by ultra-violet light (U.V.) of two strains (AD-169, C-87) of human cytomegalovirus (CMV) was determined and compared with the relative sensitivities of Herpes simplex virus (HSV) type 1 and type 2. The survival curves were multicomponent. The inactivation rates from the first component indicate that CMV (D37 dose t200 ergs/mm2) is more resistant to U.V.-inactivation than either HSV-1 or HSV-2 (D37 dose ∼90 ergs/mm2). Multiplicity reactivation (MR) could be clearly demonstrated for U.V.-irradiated CMV. MR occurred at multiplicities of infection (MOI) corresponding to 0·003 plaque-forming units (PFU) per cell of unirradiated virus. In contrast, MR for HSV was not pronounced at an MOI corresponding to 1·0 PFU per cell. These data suggest that defective particles of CMV, incapable of plaque formation before U.V.-irradiation, participate in the genetic interactions which are responsible for the MR observed.