Optimal conditions for plaque assay of echoviruses in human embryonic lung fibroblast cells

The present paper gives optimal conditions for plaque assays tn human embryonic lung fibroblast cells with 45 echoviruses including 11 fresh isolates, covering 31 serotypes. All the viruses tested except echovirus type 23 produced plaques at a high titer in the same cells by the methods described in this communication. Plaque formations by a number of strains were markedly enhanced in size or number or both by the addition of polycation.