Effect of essential oil on the first cycle of PR8 infection as determined by FFA. MDCK cells in 96-well plates were infected by oil-treated virus for 7 h, and viral NP was detected using an Alexa Fluor 488 (green) labeled antibody. Panels: (A) MDCK cells unexposed to virus, but stained with anti-NP antibody. Panels B-F cells exposed to PR8 treated with dilutions of essential oil (B) 1:1,000 (C) 1:2,000 (D) 1:3,000 (E) 1:4,000 (F) 1:5,000, (G) 1:6,000, (H) untreated PR8, (I) PR8 treated with control oil 1:1,000. Panels I-L were fluorescence images merged with corresponding brightfield images to show MDCK cell morphology (J) PR8 treated with essential oil 1:1,000, (K) PR8 treated with essential oil 1:6,000, (L) untreated PR8 (merge). Bottom panel: PR8 first cycle NP production as depicted by the percentage of cells containing detectable NP at 7 h after infection. The results represent the mean ± SEM from three independent experiments.