MDCK cell culture and cytopathogenic effect measurements

A continuous line of Madin Darby canine kidney II (MDCK II) cells was grown in minimal essential medium (MEM, Gibco, Gibco Life Technologies, Germany) supplemented with 10% fetal bovine serum (Invitrogen, Thermo Fisher Scientific, USA), 1% L-Glutamin (Sigma-Aldrich, Merck KGaA, Germany), 1% Penicillin und Streptomycin (Sigma-Aldrich, Merck KGaA, Germany). Cells were infected as described before (modified after Gaush and Smith [55]). Infection of MDCK cells was performed at 37°C for 48 hours in 96-well microtiter plates containing infection medium (MEM with 1% L-Glutamin, 0.2% BSA, 1% each Penicillin, Streptomycin and 1 mg/mL TPCK-trypsin (Sigma-Aldrich, Merck KGaA, Germany)). The viruses were serially diluted to obtain 1, 5, 10, 100 and 1000 PFU. Cytopathic effects were evaluated by light microscopy.