In: Biology
Motility is the ability of an organism to move with the help of a microtubular structure Flagella that produces whip like motion or gliding motion mainly in bacterial entities.
Semi solid agar medium is used for identifying motile bacterial organisms as they tend to give a diffused spreading growth contrary to the non motile bacteria where the growth will only be along the stab line.Sulphur Indole Motility Test is used for the characterization of Enterobacteriaceae family members which are a group of gram negative,facultative anaerobes forming acids from glucose/lactose fermentation.
In this test the motile organism will make the entire media turbid due to it's movement whereas the non motile won't show the same and will show growth only around the inoculation spot.
In addition to this if the bacteria is Sulphur positive black Colour will be seen in the inoculation tube.Red color can be seen in case of Indole positive by the action of Kovacs reagent.