TLR5 and bacterial infectious disease: Bacterial infection (or lysates) causes the delivery of ligands, such as LTA, peptidoglycan, flagellin, single-stranded (ss) RNA, double-stranded (ds) RNA and CpG DNA, to the host, which activates multiple TLRs, such as TLR1-3, TLR5, TLR7-9, TLR21, and teleost-specific TLR19 (51) and TLR22 (52).