The idea of knowing whether a suspected organism is motile or not can be of great use in bacteria identification knowing that not all bacteria are motile meaning not all bacteria possesses flagella.
Motility is one characteristic used in the identification of bacteria and also an evidence of possessing structures different flagella structural arrangement such as peritrichous flagella, polar flagella and/or a combination of both
A flagellum is a lash-like appendage found in certain bacterial and eukaryotic cells. It has a primary role of locomotion helping these flagellated bacteria to move from one area to another
Principle of the Hanging drop technique
Based on the invention of the suspended drop of the inoculum on a cover slide over a cavity slide or normal slide which is supported on a ring of plasticine or vaseline (Petroleum jelly)
Materials required for the Hanging drop technique
- Cover glass
- Depression slide
- Toothpick or applicator stick
- Petroleum jelly or vaseline
- Inoculum (Probably a broth)
- Wire Loop
Procedure of Hanging drop technique
- Using a toothpick, place a small dab of Vaseline or petroleum jelly in each corner of a clean cover glass handling the cover glass by its edges in order to avoid fingerprints.
- Now,aseptically transfer a loopful of a liquid bacterial culture (Inoculum) into the center of the cover glass. Do not spread the drop!
- Carefully lower depression slide with depression facing down and cover the inoculum such that the vaseline attaches the cover class to the depression slide
- Now you can quickly invert depression slide.This will enable the drop of the inoculum to be suspended from the cover glass inside the concave hollow of the depression slide.
- Using the 10x then 40x objectives and coarse adjustment knob, focus on the edge of the hanging drop and observe for motile organisms.
- Make sure the iris diaphragm of the condenser is sufficiently closed in order to give a good contrast otherwise the organisms will not be seen
- Motile cells move independently. All other cells seem to vibrate in place ( like Brownian motion).
- Also observe slide immediately after preparation as motility decreases over time. Also, as drop dries out and recedes, water currents will appear to herd and move bacteria in the same direction – this has nothing to do with motility!
List of Motile bacteria and non motile bacteria
|Motile Bacteria||Non Motile|
|Listeria monocytogenes||Klebsiella pneumoniae|
|Vibrio cholerae||Yersinia pestis|
|Pseudomonas aeruginosa||Shigella boydii|
|Proteus mirabilis||Streptococcus pneumoniae|
|Escherichia coli||Shigella sonnei|
|Helicobacter pylori||Bacteroides Fragilis|
|Salmonella enterica||Haemophilus species|
|Treponema pallidum||Mycobacterium tuberculosis|
|Campylobacter jejuni||Clostridium perfringens|
|Bacillus cereus||Bacillus anthracis|
|Clostridium tetani||Salmonella gallinarum|
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