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

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Objectives of Motility Test

  • To determine the motility of bacterium.
  • To differentiate between motile and non motile bacteria.

Principle of Motility Test

Motility is the ability of an organism to move by itself by means of propeller-like flagella unique to bacteria or by special fibrils that produce a gliding form of motility. Motile bacteria move using flagella, thread-like locomotor appendages extending outward from the plasma membrane and cell wall either single flagellum or multiple flagella. Each flagellum has a very rigid, helical structure, and actual motility results from the rotation of the flagellum in a manner similar to that of a boat propeller. Motility by the bacterium is demonstrated in a semi-solid agar medium. The medium mainly used for this purpose is SIM medium (Sulphide Indole Motility medium) which is a combination differential medium that tests three different parameters, Sulfur Reduction, Indole Production, and Motility. This media has a very soft consistency that allows motile bacteria to migrate readily through them causing cloudiness. The inoculum is stabbed into the center of a semisolid agar deep using a sterile inoculating needle.  Bacterial motility is evident by a diffuse zone of growth extending out from the line of inoculation. Some organisms grow throughout the entire medium, whereas others show small areas or nodules that grow out from the line of inoculation. The non-motile bacteria will only grow in the soft agar tube and only the area where they are inoculated.

Media Used in Motility Test

SIM Medium

Composition per liter:

Pancreatic digest of casein…………………………..20.0g

Peptic digest of animal tissue………………………..6.1g

Agar…………………………………………………………..3.5g

Fe(NH4)2(SO4)2·6H2O………………………………….0.2g

Na2S2O3·5H2O…………………………………………….0.2g

pH 7.3 ± 0.2 at 25°C

Procedure of Motility Test

  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.

Result Interpretation of Motility Test

Motility Test- Principle, Procedure and Results

Motile: organisms will spread out into the medium from the site of inoculation, diffuse zone

Non-motile:  organisms remain at the site of inoculation

Limitation of Motility Test

Some organisms will not display sufficient growth in this medium to make an accurate determination, and additional follow-up testing is required.

Quality Control of Motility Test

Positive: Escherichia coli (ATCC25922)

Negative: Staphylococcus aureus (ATCC25923)

References

  1. Tille P.M. 2014. Bailey and Scott’s diagnostic microbiology. Thirteen edition. Mosby, Inc., an affiliate of Elsevier Inc. 3251 Riverport Lane. St. Louis. Missouri 63043
  2. Pelczar MJ, Chan E.C.S, Krieg NR. 1958. Microbiology. Tata McGraw Hill Education Private Limited. 7 West Patel Nagar. New Delhi 110 008.

About Author

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Sagar Aryal, PhD

Dr. Sagar Aryal is a microbiologist, researcher, and science communicator from Nepal. He is also co-founder and Research Head of the Department of Natural Products at the Kathmandu Research Institute for Biological Sciences (KRIBS), where he leads research on natural product discovery and microbial biodiversity. Dr. Aryal earned his Ph.D. in Microbiology from Tribhuvan University, Kathmandu, Nepal, in 2025, supported by a DAAD Research Grant and a University Grants Commission (UGC) Nepal Ph.D. Fellowship. His research interests include Actinomycetes, Myxobacteria, microbial taxonomy, and natural products, particularly the discovery of bioactive compounds with potential pharmaceutical applications. He isolated and identified Nocardia nepalensis, a novel bacterial species from Nepal, contributing to understanding microbial diversity in the region. Dr. Aryal has published more than 16 research articles in international journals and contributed three book chapters to established academic publications. He has presented scientific research findings and developed international research collaborations through visits to more than 18 countries across Asia, Europe, North America, and Oceania. From 2023 to 2025, he served as the American Society for Microbiology (ASM) Young Ambassador to Nepal. Since December 2025, he has served as an Editorial Board Member of Scientific Reports, a Nature Portfolio journal. In recognition of his scientific contributions, Dr. Aryal received the NAST Science and Technology Youth Award 2025 from the Nepal Academy of Science and Technology. He previously received the Frs. Locke and Stiller Research Award (LSRA) for the 2017-2018 cycle from St. Xavier's College, Kathmandu, and a Nepal Academy of Science and Technology (NAST) Research Grant for 2017-2018. Alongside his scientific career, Dr. Aryal has more than 15 years of experience in blogging, content writing, and search engine optimization (SEO).

3 thoughts on “Motility Test- Objectives, Principle, Procedure, Results, Limitation”

  3. Some times growth is present on the upper side of tube but whole tube is not turbid..result will be positive or negtive ?

    Reply

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