FIG 4 .

Host origin and subtype affect the susceptibility of influenza A virus to lipopolysaccharide. (A) Phylogenetic tree constructed using the hemagglutinin (HA) gene of nine influenza A viruses with influenza B virus included as an outgroup. Bootstrap percentages for the internal nodes are displayed. The bar shows the evolutionary distance (number of base substitutions per site). (B) Stabilities of these viruses after incubation for 1 h at 48°C in lipopolysaccharide (LPS) or water control (n = 3). Data are represented as means plus SEM. Statistical significance was assessed using a Student’s t test to compare the values for virus treated with LPS and water control. **, P  < 0.01;  *, P < 0.05. BDL, below detectable limit of 0.025% initial titer. (C) Ratio of stability in LPS and water of the viruses across hosts and subtypes. The value for each replicate is represented as a circle. (D) Schematic representation summarizing the results.