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we assess on the presence of co-isolated viruses in influenza virus isolates recovered from MDCK cells. This article provides more specific data about the kind and frequency of co-infecting respiratory viruses in human influenza virus-containing samples and about the fate of such co-infecting viruses during passage in MDCK cells. Nasal or pharyngeal samples from the 2007/2008 influenza season were provided by a clinical diagnostic laboratory located in Stuttgart, Germany. These samples from patients with acute respiratory tract infections were obtained by physicians mainly from Southern Germany and were sent to the diagnostic laboratory in liquid virus transport medium. Aliquots of the clinical specimens (with a laboratory number as an anonymous identifier) were sent to Novartis Vaccines in Marburg, Germany, by a weekly courier service. During transportation AZD2281 cell line the samples were stored at 2–8 °C. Directly after BMS-777607 research buy receipt of the samples, MDCK 33016PF cells were inoculated (details see further below) with sample material. The cultures were harvested after 3 days of incubation, and the cell-free supernatants were aliquoted and stored at ≤−60 °C until further use. MDCK 33016PF suspension cells from Novartis working cell bank were cultivated in 500 ml disposable spinner

flasks (Corning) in CDM medium, a chemically defined growth medium used for cell propagation (MDCK 33016 CDM, Lonza) and passaged at 3–4-day intervals. During those 3–4 days the cells grew from an initial seeding density of 1 × 105 cells/ml to densities between 1.0 and 1.5 × 106 cells/ml. For infections 4.5 ml

cells were seeded in 50 ml filter tubes (TPP, Transadingen, Switzerland) at a cell density of 0.8–1.2 × 106 cells/ml. Cells in CDM medium were diluted at a 30/70% ratio into MDCK 33016 PFM medium (“protein-free else medium”, Gibco Invitrogen) supplemented with 0.5% of a penicillin/streptomycin solution (Sigma) and 900 IU/ml trypsin. To obtain a total culture volume of 5 ml, the added viral inoculum was diluted in 0.5 ml infection medium and was pre-diluted by several log10 steps, starting with a total dilution of at least 1:100. Inoculated cultures were then incubated at 33 °C for 3 days in a 5% CO2 atmosphere in a ISF-1-W shaker incubator (Kuhner, Birsfelden, Switzerland). For virus harvests the cells were separated by centrifugation (800–1000 × g for 10 min) and the supernatant was recovered. Unless used freshly, e.g. for haemagglutination tests and subsequent passaging, aliquots of the supernatant were frozen at ≤−60 °C. Haemagglutination (HA) testing was done with harvested material to define the starting material for the next passage. HA testing was performed in U-bottom microwell plates (Greiner Bio-One) using 100 μl of a serial log2 dilution in PBS (pH 7.0) of the test samples and 100 μl chicken or guinea pig red blood cells (0.5% in PBS pH 7.0).