Flagella
Many bacteria are capable of mortality due to the presence of specialised structures called flagella. The shape of the flagella about the bacterium is used in classification and identification.
The following flagella arrangements may be found.
- Athrichous - no flagella present.
- Monotrichous - a single flagellum at one pole.
- Amphitrichous - single flagella at both poles.
- Lophotrichous - two or more flagella at one or both poles of the cell.
- Peritrichous - completely surrounded by flagella.
Motility Test -
This test is used to determine if organisms are motile by means of flagellum. The location of the
flagella is determined by the bacterial species. Non-motile bacteria do not possess flagellum.
Bacterial motility must be distinguished from Brownian motion. Feebly motile bacteria may require prolonged observation of individual cells. Motility results are difficult to determine for anaerobic bacteria. Only a positive result is significant. Some bacteria are motile at one temperature and non motile when incubated at another.
Some bacteria become less motile in old cultures.
Materials :
- Staphylococcus aureus ans Proteus vulgaris culture.
- Inoculation needle.
- Motility Test Agar
Procedures :
- Inoculate the motility test agar with 1 of the bacteria listed above.
- Use a straight inoculation needle.
- Employing aseptic technique, stab down into the centre of the agar to about one-half of the way down.
- Withdraw needle carefully along the same stab line.
- Repeat with the other bacteria listed. Incubate at 37°C for 24 hrs. Label this
tube.
Results :
Non-motile Organisms have bacterial growth along the line of the stab.
Motile Organisms have spreading or diffused bacterial growth from the stab line.
Hanging Drop Preparations -
Procedure :
- Using sterile technique, transfer a loopful of culture to the centre of a clean
glass cover slip.
- Roll out 2 plasticine strips (ensure that they are not thick and about the length
of coverslip.
- Gently press a slide against the coverslip, turn it over quickly, leaving the drop suspended in the middle of the cover slip.
- Examine the culture under high power objectives. Close the diaphragm
opening, because the bacteria are unstained and they will be difficult to locate.
- Focus on the edge of the droplet before attempting to locate individual cells. After the bacterial cells have been located, study them carefully for evidence of motion.
Results :
An example of a hanging drop slide