Optimization of trypsins for influenza A/H1N1 virus replication in MDCK SI-6 cells, a novel MDCK cell line.

•SI-6 cells were obtained by extensive passage of MDCK cells with a bacterial enzyme.•Bovine, porcine, fungal and recombinant trypsins were compared for Flu A/H1N1 growth.•Bovine and porcine trypsins were the most suitable for virus growth in SI-6 cells.•The virus grew better in SI-6 than in MDCK cells with bovine and porcine trypsins.•SI-6 cells may be suitable for influenza vaccine production.