Question

Explain why a control tube with a nonmotile bacterial species is necessary for reliable determination of bacterial motility by a) the hang drop preparation and b) the motility test agar preparation.

Answer 1

Motile Bacteria : A bacteria which have intrinsic ability of movement is surroundig media. Motile bacteria moves about with structure called Flagella.

Non-motile Bacteria : A bacteria which do not have intrinsic ability of movement is surroundig media, in which it remain suspended.

Moblity of bacteria can be determine by biochemical tests as well as microscopic analysis. Hang drop preparation & motility test agar are microscpic analysis process with fresh bacterial culture. While performing wet mount prepataion the shape and size of the bacteria can be observerd easily, as the suspension is pressed between the slide and the cover slip, but the motility of the bacteria may be hampered, that's why the Hang drop preparation & motility test performed for the clear observation of motility of bacteria, beside their shape and size.

In Hang drop preparation, a very small amount of bacterial suspesion is hung from center of the cover slip in to the cavity, the hanging drop obsereved under microscope using oil immersion objective. If cells have erratic movement of bacteria in surrounding media, the bacteria is said to be Motile bacteria.

Motility Agar test (TTC) : Bacterial motility can be visualize on media having agar concentration of 0.4% or less or semi solid media. Motility agar is semi solid media that elicits growth and which allows the bactera to move. As a result, the motile bacteria shows pink or red diffuse growth throught the medium.

The inoculated control tube is incubate aerobicallly and used to asset the stability of media as well as the sterility of the complete medium.