HANGING DROP METHOD

HANGING DROP METHOD

AIM

            To perform the Motility test of bacteria by Hanging Drop Method.

PRINCIPLE  

            The mobility in bacteria is largely credited to presence of large hair-like appendages over the body called as “Flagella”. These are the locomotor organ of bacteria. The process of staining the flagella is very tedious. Also it is very difficult to observe in the normal compound microscope. Bacterial movement must be distinguishable from the “Brownian movement” (the movement of small invisible particles in any medium). However, the presences of bacteria/activity of flagella can be visualized by the ability of microbe to move in growth medium or by Hanging drop technique.

            The Hanging drop technique is a well-established method for examining living, unstained, very small organisms. The traditional procedure employs a Glass slide with a Circular concavity in the centre into which a drop of fluid, containing the ‘microorganisms’, hangs from a coverslip.

            A small drop of bacteria suspension is hung from the center of a Cover slip into the cavity of a Cavity slide. The Hanging drop is observed under a Microscope using low power objective under dark background. If the bacteria are motile, cells can be seen to have erratic movement in the surrounding medium. In contrast, if it is non-motile, its cells remain static in the medium without any movement or may show Brownian movement resulting from the bombardment by the water molecules in the medium, on the bacteria cells.

MATERIALS REQUIRED

i.       24 hours culture of Bacteria

ii.     Bunsen burner

iii.   Cavity slide

iv.   Cover slip

v.     Vaselin or Paraffin wax

vi.   Microscope.

PROCEDURE

a)     Place a small drop of bacterial culture in the center of a coverslip and place a little Vaselin in the cavity slide over the coverslip with the hanging drop suspended in the depression.

b)     Bring the edge of hanging drop into focus with 40 X objective and absorb the motility.

Figure – 1: Hanging drop method

OBSERVATION AND RESULTS

            If the bacteria are motile, bacterial cells movement have been observed near the edge of the Coverslip in the Cavity slide.