Overview
Bacterial flagella are proteinaceous appendages that rotate to produce motility; clinical laboratories usually infer them from motility phenotypes rather than direct routine visualization.
Classification
| Arrangement term | Pattern | Lab use |
|---|---|---|
| Monotrichous | Single polar flagellum | Textbook differential language |
| Lophotrichous | Polar tuft | Rarely visualized routinely |
| Amphitrichous | Both poles | Rarely visualized routinely |
| Peritrichous | Many around cell | Common enteric motility pattern |
Morphologic Features
Flagella are generally not seen on Gram stain. Motility and swarming are the practical morphologic/phenotypic expressions.
Laboratory Characteristics
- Perform wet mounts on fresh suspensions when used
- Incubate motility media per SOP time/temperature
- Isolate through swarming films before final ID when needed
Reference Intervals
Qualitative only. Motility medium reading windows are method- and SOP-specific.
| Result | Interpretation | Caveat |
|---|---|---|
| Directional wet-mount motion | Motile | Exclude Brownian motion |
| Stab-line clouding | Motile | Avoid reading contaminated tubes |
| Swarming film | Strong motility phenotype | Confirm species by ID |
| Nonmotile | No motility under test conditions | May be technical or true |
Clinical and Laboratory Significance
Motility refines identification pathways. Clinical significance remains a function of organism identity and specimen site, not motility alone.
Differential Considerations
Differentiate swarming Proteus-like phenotypes from other surface spreaders by completing identification; differentiate true motility from Brownian motion.
Comparison Tables
Motility vs Brownian motion
| Feature | True motility | Brownian motion |
|---|---|---|
| Appearance | Directional runs/tumbles | Vibratory jiggling |
| Net displacement | Yes | Minimal |
| ID value | Useful clue | Ignore as motility |
Classification Frameworks
Flagellar arrangement terms are morphologic descriptors, not WHO disease classifications.
Laboratory Notes
- Motility test availability and preferred methods vary by laboratory
- Do not equate educational Proteus swarming examples with universal species proof
- Avoid pathogenicity ranking based solely on motility results
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
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