Protein distance tree of H1 antigens. The tree displays the inferred amino acid sequence distances between full H1 antigens. The label displays the H1 antigen, and the Salmonella serotype or subgroup from which the sequence was obtained. Esherichia coli fliC-H7 sequence was used to root the tree. Bootstrap values are displayed at major nodes. Sequences labelled with _a, _b or _c indicate an H1 allele found to be encoded by multiple sequences (Additional file 2).