Growth of Recombinant H5N1 Influenza Viruses Before and After Passaging in MDCK Cells.

aAmino acid numbering is based on N2 NA [43].
bMDCK cells were infected with recombinant viruses at an MOI of 0.001 PFU/ml and virus yield was determined after 72 h incubation at 37°C. Plaque size of any 10 plaques was measured by the Finescale® comparator (Los Angeles, CA, USA). The HA and NA genes were sequenced after the 3rd passage. The emergence of different subpopulations indicated genetic instability.
* P<0.01 compared to WT virus from the same passage (one-way ANOVA).
° P<0.01 compared to plaque size after the first passage (unpaired two-tailed t-test).