We next tested this dual infection model in WT and TLR9-/- mice and observed a significant survival difference between TLR9-/- and WT mice, where 77% of TLR9-/- mice survived the secondary bacterial infection compared to 33% of WT mice (Fig 4B; data represent n = 13 mice combined from 2 separate survival assays matched for sex and starting weight). This evidence concerns the gene TLR9 and infection.