microbiology

• Motility


  The ability of an organism to move by itself
• Motility


  • Linked with chemotaxis, the ability to orient along certain chemical gradients
  • Eukaryotic cells can move by means of different locomotor organelles such as cilia, flagella, or pseudopods
  • Prokaryotes move by means of propeller-like flagella unique to bacteria or by special fibrils that produce a gliding form of motility
  • Almost all spiral bacteria and about half of the bacilli are motile, whereas essentially none of the cocci are motile
• Arrangement of Flagella


  • Monotrichous (Vibrio cholerae)
  • Amphitrichous (Spirillium volutans)
  • Lophotrichous (Pseudomonas fluorescens)
  • Peritrichous (Escherichia coli)
• Components of Flagella


  • Filament – Composed of a protein called flagellin
  • Hook – Base of filament near cell wall
  • Basal Body – Anchors filament & hook to cell wall
• Types of movement


  • Run: straight line movement occurs when the flagella rotates counterclockwise
  • Tumbles: turning the direction by clockwise movement of the flagella
• Types of Bacterial Motility

  • Brownian Movement – results from the random motion of the water molecules bombarding the microbial cells and causing them to move e.g. Saccharomyces cerevisiae (yeast), Staphylococcus aureus (bacteria)
  • True Motility – independent movement brought by different mechanisms for self-propulsion e.g. Bacillus megaterium, Escherichia coli
• Tests to determine bacterial motility

  For non-pathogenic bacteria: Wet Mount, Hanging Drop.

  
  

  For pathogenic bacteria: Soft-agar stabbing (culture-based method)
• Wet Mount


  Uses glass slides and cover slips. Advantages: easier to prepare. Disadvantages: t
• Tests to determine bacterial motility

  1. Wet Mount

  2. Hanging Drop

  3. Soft-agar stabbing (culture-based method)
• Wet Mount


  1. Uses glass slides and cover slips

  2. Advantage/s: easier to prepare

  3. Disadvantage/s: tend to dry out quickly under the heat of the microscope light, thus, it is useful for short-term observation only
• Hanging Drop


  1. Uses depression slides and cover slips

  2. Advantage/s: allows for longer-term observation and more reliable observation of motility

  3. Disadvantage/s: more complex to prepare

  4. Disadvantage of both wet mount and hanging drop: specimen is unstained, no contrast between specimen and background

  5. Solution: use stains that will not kill the cells or distort the cells and their structures, use phase contrast microscope
• Soft-agar stabbing (culture-based method)

  1. Uses wire needle, alcohol lamp, and motility medium* in test tubes

  2. *Different modifications of the motility media are available and may be used depending on the purpose
• Results of Soft-agar stabbing (culture-based method)

  • Positive: Diffuse, hazy growths that spread throughout the medium rendering it slightly opaque
  • Negative: Growth that is confined to the stab-line, with sharply defined margins and leaving the surrounding medium clearly transparent
• Principle of the test (Source: Difco Manual)

  1. Motility Test Medium

  2. Bacterial motility can be observed directly from examination of the tubes following incubation. Growth spreads out from the line of inoculation if the organism is motile. Highly motile organisms provide growth throughout the tube. Growth of nonmotile organisms only occurs along the stab line. TTC (triphenyltetrazolium chloride) may be added to facilitate the detection of motility. TTC is a redox indicator that is colorless in the oxidized form but becomes an insoluble red precipitate when reduced