: a polymeric protein that is the chief constituent of bacterial flagella and that determines the specificity of the flagellum in eliciting an immune response
: a polymeric protein that is the chief constituent of bacterial flagella, that forms helical chains around the hollow core of the flagellar filament, that determines the specificity of the flagellum in eliciting an immune response by its amino acid sequence, and that within any one serogroup can vary between two antigenic states by switching between the expression of two different genes