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Sambucus nigra Extracts Inhibit Infectious Bronchitis Virus at an Early Point during Replication
Vaccination against infectious bronchitis virus (IBV), a pathogenic chicken coronavirus, is not wholly effective. The secondary compounds of plants may provide better treatments or preventions against IBV. Crude ethanol extracts of Rhodiola rosea roots, Nigella sativa seeds, and Sambucus nigra fruit were tested for anti-IBV activity. Cells and virus were pretreated with the highest possible non-cytotoxic dose of individual plant extracts, followed by infection in the presence of extract. Cells and supernatants were harvested separately following an additional 24h incubation with extract. Virus titers from infected cells treated with R. rosea and N. sativa extracts were not substantially different from infected cells treated with solvent alone. However, treatment with S. nigra extracts reduced virus titers by three orders of magnitude at an MOI of 1 in a dose-responsive manner. Infection at a low MOI reduced viral titers by seven orders of magnitude and pretreatment of virus alone was necessary, but not sufficient, for full virus inhibition. Electron microscopy of virions treated with S. nigra extract showed compromised envelopes and the presence of membrane vesicles, suggesting a mechanism of action. These results demonstrate that S. nigra can inhibit IBV at an early point in infection. Future studies will address the factors, in addition to pre-treatment of virus, that are necessary for full virus inhibition. Overall these studies identified a plant extract with previously unknown effects against IBV and could potentially lead to effective treatments or prevention of this or similar coronaviruses.