Evaluation of mixed cell types and 5-iodo-2'-deoxyuridine treatment upon plaque assay titers of human enteric viruses.

Four continuous cell lines, BGM, L-132, HEL-299, and RD, were compared both when cultured separately and as mixtures for use in plaque assay titrations of human adenovirus 1 and six human enterovirus serotypes. The effect of incubating these cell cultures in media containing 5-iodo-2'deoxyuridine (IDU) prior to inoculation with virus was also studied. The use of mixed-cell cultures revealed cell line-dependent synergistic effects as well as inhibitory effects. These effects were strongly virus dependent. In particular, enterovirus 69 did not form plaques on any of the four cell lines when cultured independently. However, it did form plaques on nearly all of the cell lines when cultured as mixtures. Contrary to this effect, when BGM cells were used in combination with the other cell lines, plaque counts for adenovirus 1 were greatly reduced. The effect of IDU pretreatment was also virus and cell line specific and enabled some viruses to form plaques on cell lines when they otherwise would not. Overall, IDU pretreatment resulted in an approximate twofold increase in plaque titers over those obtained without treatment.