Bacterial flagella ; Function & medical importance

Bacterial flagella are long, thin (about 20 nm), whip like appendages that move the bacteria towards nutrients and other attractants.  Flagella are free at one end and attached to the cell at the other end.  Flagellum can never be seen directly with the light microscope but only after staining with special flagella stains that increase their diameter.

The long filament of flagella is composed of many subunits of a single protein, flagellin, arranged in several intertwined chains. The energy for movement, the proton motive force, is provided by ATP.

Flagellar motion in Bacterial Cells

Key Information: Most of the cocci (e.g. Staphylococci, Streptococci etc) don’t have flagella so they are non-motile.
Functions of Bacterial Flagella
Many prokaryotes are motile, and the majority of motile prokaryotes moves by means of flagella.
Medical Importance of Flagella 

• Role in Pathogenesis: Escherichia coli and proteus spp are common causes of Urinary tract infections. The flagella of these bacteria help the bacteria by propelling up the urethra into the bladder.
• Roles in Organism identification
  • Some species of bacteria, eg. Salmonella species are identified in the cilinical laboratory by the use of Specific antibodies against flagellar proteins.
  • Organisms such as Vibrio cholerae (darting motility) and Proteus species (swarming growth in common culture media) are easily identified by their characteristics motility pattern