Motility Patterns of Bacteria: Tumbling, Darting, Swarming, and the Key Exceptions

A wet mount from an overnight broth shows cells that roll end-over-end rather than swim in a straight line. That tumbling is not incidental; in the right clinical context (a neonatal sepsis or meningitis workup) it points straight at Listeria monocytogenes. Motility is not just present-or-absent; the pattern of movement, and the temperature at which it appears, can name the organism. This article maps those patterns and, just as importantly, the exceptions where a normally motile organism goes still.

When you read about the structure of bacterial cells, you might have learned about flagella and the different types of flagellar arrangements found in gram-negative bacteria. Most Gram-positive bacteria are atrichous (without flagella), so they are non-motile (Enterococcus gallinarum and E. casseliflavus/E. flavescens, the gram-positive, catalase negative cocci, generally are motile. )

Figure: Test for Bacterial Motility: Center (Non-motile); Corners (Motile)

So when it’s about bacterial motility, we mostly discuss Gram-negative bacteria. Motility patterns of Gram-negative bacteria are also used for their identification.

You might have appreciated the colony of Proteus spp in blood agar and MacConkey agar and identified it with its characteristics swarming patterns.

So in this blog post, I am sharing information about the characteristic motility patterns of some bacteria. You will also find information about those bacteria which become non-motile in specific conditions and about some great exceptions to motility characteristics;

Characteristics types of  Bacterial Motility

Key non-motility exceptions to memorize: Bacillus anthracis (non-motile among otherwise-motile Bacillus); Klebsiella pneumoniae; Shigella; Acinetobacter; Yersinia (motile only at 20–28°C). Motile cocci exception: Enterococcus gallinarum and E. casseliflavus (most other Gram-positive cocci are non-motile/atrichous).

Characteristics Motility Patterns of Selected Organisms

1. Alcaligenes are motile by peritrichous flagella.
2. Acinetobacter are non-motile.
3. Bacillus spp. should be motile; non-motility is a clue to Bacillus anthracis.
4. Campylobacters are small delicate, spirally curved, motile Gram-negative bacteria.  They show characteristic rapid corkscrew-like motility.
5. E. coli: Most are motile by peritrichous flagella. Alkalescens-Dispar group i.e.A-D group is non-motile.
6. Enterococcus casseliflavus and E. gallinarum are motile (the motile-cocci exception); E. faecium and E. faecalis non-motile.
7. Helicobacter: Helicobacter spp is motile by a tuft of flagella (up to 4-7 sheathed flagella are present at one end).
8. Listeria spp: It is motile with a characteristic tumbling and rotating motility in broth cultures when grown at 18- 25°C but not motile or minimally motile when grown at 35-37°C. Listeria gives "umbrella"-shaped growth near the top of a semisolid tube at 25°C.
9. Proteus spp: P. mirabilis and P. vulgaris are actively motile (swarming motility). Motility is not as easily observed at 35–37 ºC as at room temperature (20–28 ºC).
10. Pseudomonas spp: Most species of Pseudomonas are motile except Pseudomonas malli using one or more flagella.
11. Salmonella spp: Most strains are motile except Salmonella Gallinarum and Salmonella Pullorum
12. Spirilla are motile with groups of flagella at both ends.
13. Spirochaetes (Treponema, Borrelia, Leptospira): Are motile by bending and rotating body movements.
14. Trophozoites of protozoan parasites Entamoeba histolytica and Giardia lamblia (move by flagella and an undulating membrane) etc show motility in wet preparation.
15. Vibrio cholerae: Vibrio cholerae are motile with the single polar flagellum and show rapid darting  (“Shooting Star”) motility.
16. Yersinia enterocolitica is motile when grown at 20- 28°C but non-motile at 35-37°C.

How to Remember

Name the swim, name the bug. Tumbling = Listeria. Darting shooting-star = Vibrio. Swarming sheets on agar = Proteus. Corkscrew = spirochetes and Campylobacter. The movement is often the fastest presumptive clue you have.

"Cold swimmers": Listeria and Yersinia. Both swim at 20–25°C and stall at 37°C. Body temperature switches their flagella off.

The still ones that should surprise you. Most Bacillus swim — a non-motile one raises anthracis. Most Gram-positive cocci sit still — a motile enterococcus points to gallinarum/casseliflavus. The exception is the exam point.

References

1. Madigan MT, Bender KS, Buckley DH, Sattley WM, Stahl DA. Brock Biology of Microorganisms. 15th ed. Pearson; 2018.
2. Procop GW, Church DL, Hall GS, Janda WM, Koneman EW, Schreckenberger PC, Woods GL. Koneman's Color Atlas and Textbook of Diagnostic Microbiology. 7th ed. Philadelphia: Wolters Kluwer; 2017.