Objective: Titration of viruses is important to determine the quantity of virus in vaccine development, master virus seed stock preparation, viral vector studies and virus replication. In this study, we compared the CCID50% and plaque assay as a standard titration method for rotavirus (RF) and HSV-1. Methods: The MA104 and Vero cells were inoculated by RF and HSV-1 in 6-and 96-well plates. Following infection and adsorption, the optimal time for the cytopathic effect caused by the viruses was

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... ted and the results compared. Results: The CPE (Cytopathic Effect) of RF was observed in less than 18 hours, which increased until 72 hours after inoculation. In HSV-1, the CPE was observed 24 and 72 hours after inoculation. The virus titration in the plaque assay was monitored at 96 hours post-infection for RF and at 72 hours post-infection for HSV-1. In both viruses the plaque titer method was lower than the CCID50 method, since the results indicated that 1 CCID50% was equal to 0.7 PFU. Conclusion: The plaque assay is one of the most accurate methods for viral titration. For the plaque assay, individual lesions may be isolated, which the plaques can be counted. The CCID50% method is not applicable for purification of homogenous viruses, nor is this technique reproducible.