Bacterial Flagella: Structure, importance and examples of flagellated bacteria

Flagella are long, whip like appendages that move the bacteria toward nutrients and other attractants.  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

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. Arrangement and Types of Flagella The number and location of flagella are distinctive for each genus. There are four types of flagellar arrangement.

  1. Monotrichous: Single polar flagellum e.g. Vibrio cholerae  (Mneomonics: Mono means one)
  2. Amphitrichous: Single flagellum at both ends e.g. Alcaligenes faecalis  (Mneomonics: Remember: the characteristics of Amphibians: live both in land and water) flagellar arrangement of bacteria
  3. Lophotrichous: Tuft of flagella at one or both ends e.g. Spirilla
  4. Peritrichous: Flagella surrounding the cell, e.g. Typhoid bacilli (Mneomonic: Remember Periphery)
Spirillum and its flagellar arrangement

Spirillum and its flagellar arrangement

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.
  • mercedita decosto

    how does bacterium move according to the arrangement of their flagellum/ flagella? to what direction? do they move fast of slow?