The Structure Of A Prokaryotic Flagellum

The filament is composed of the globular protein flagellin, which is arranged in several intertwined chains that form a helix around a hollow core.
 
Flagellin can vary in structure and is used to identify some pathogenic bacteria serologically. The flagellar antigens are referred to as H antigens.
 
E. coli may express any of at least 50 different variants; serovars (serological variants) identified as O157:H7 are associated with food borne epidemics ( O antigens are somatic antigens and are lipopolysaccharide complexes associated with the cell wall).
 
Flagella are anchored by pairs of rings associated with the plasma membrane and cell wall. Gram positive bacteria have only the inner pair of rings.