Motility Test- Objectives, Principle, Procedure, Results, Limitation

The motility test is a microbiological test that is used to determine whether a bacterium can move by itself or not. Motility is an important characteristic of bacteria, as it can affect their pathogenicity, virulence, and survival in different environments. The motility test can also help to differentiate between different types of bacteria based on their patterns of movement.

The motility test is based on the ability of bacteria to move by themselves using flagella or fibrils. Flagella are long, thin, whip-like appendages that rotate like propellers and push the bacteria through the medium. Fibrils are short, hair-like structures that glide along the surface of the medium. Bacteria that have flagella or fibrils are called motile, while those that lack them are called non-motile.

The media used in the motility test are semi-solid agar media that allow the movement of motile bacteria through them. The most commonly used medium is SIM medium (Sulphide Indole Motility medium), which is a combination differential medium that tests three different parameters: sulfur reduction, indole production, and motility.

• Pancreatic digest of casein: 20.0 g
• Peptic digest of animal tissue: 6.1 g
• Agar: 3.5 g
• Ferrous ammonium sulfate: 0.2 g
• Sodium thiosulfate: 0.2 g
• Distilled water: 1000 ml
• pH: 7.3 ± 0.2 at 25°C

1. With a sterile straight needle, touch a colony of a young (18 to 24 hour) culture growing on agar medium.
2. Single stab down the center of the tube to about half the depth of the medium.
3. Incubate at 35°-37°C and examine daily for up to 7 days.

The results of the motility test can be observed by examining the appearance of the SIM medium after incubation. The motility of the bacteria can be inferred by the presence or absence of a diffuse zone of growth radiating from the stab line.

The motility test using SIM medium has some limitations that should be considered when interpreting the results. Some of these limitations are:

Quality control is essential to ensure the accuracy and reliability of the motility test results. Quality control measures include the following steps:

Positive and negative controls are essential for the validity and reliability of the motility test. They help to verify that the medium, the inoculation technique, and the incubation conditions are appropriate for detecting motility.

We are Compiling this Section. Thanks for your understanding.