N. sativa and R. rosea extracts do not inhibit IBV, while S. nigra extracts do. A – D) Cells were pretreated for 24 h and virus for 20 min with 3.75 × 10-4 g/ml N. sativa extract, 1.5 × 10-4 g/ml R. rosea extract, 4.0 x 10-3 g/ml S. nigra extract, or solvent alone prior to infection in the presence of extract. The same concentration of extract was also present during virus absorption to cells. Cells were then treated for an additional 24 h p.i. with the same concentration of extract. Independent infections with IBV were performed three times at an MOI of 0.1, with two replicates per assay. E) Cells were treated as for A – D, except that different concentrations of S. nigra extract were used, as indicated. Additionally, IBV infections were performed at an MOI of 1. A, B, C, E) Quantitation of virus titers at 24 h p.i. was done by plaquing in duplicate using neutral red staining. D) Visualization of viral CPE was done at 24 h p.i. via light microscopy. A) N. sativa, B) R. rosea, C – E) S. nigra.