Bluetongue virus propagation and plaque assay: variation due to medium and serum supplement

Two base media, minimal essential medium (MEM) and RPMI 1640, were supplemented with a variety of serum extenders and/or substitutes for the purpose of defining a medium formulation capable of supporting good cell (VERO) growth and virologic assays. Bluetongue virus (BTV), the prototype Orbivirus in the Reoviridae, was used in all studies. In general, VERO cells grown in RPMI performed better than those grown in MEM relative to cell growth, virus production and plaque assay. RPMI was better for supporting cell growth when serum extenders (NuSerum or SerXtend) were employed as supplements. Relative to virologic techniques, cells grown in RPMI produced higher virus titers in both propagation studies and plaque assays. The interval from infection to greater than 90% cytopathic effect (CPE) was consistently shorter with RPMI as the base medium. Cell cultures supported with RPMI base medium, supplemented with 3.5% FBS with SerXtend, provided the best overall performance relative to: (a) amount of virus produced by infected cell monolayers, (b) sensitivity to productive infection under overlay conditions (revealed the highest titer of a standard virus stock) and (c) plaque assay quality including cell quality, plaque size and plaque clarity.