Which of the following is the most common type of bacterial flagella arrangement in motile bacteria?

Explanation

## Bacterial Flagella Arrangements **Key Point:** Peritrichous flagella (distributed all over the cell surface) is the most common arrangement found in motile bacteria, particularly among Gram-negative rods like *Escherichia coli* and *Salmonella*. ### Classification of Flagella Arrangements | Arrangement | Location | Examples | Frequency | |---|---|---|---| | **Peritrichous** | All over the cell surface | *E. coli*, *Salmonella*, *Proteus* | Most common | | Monotrichous | Single flagellum at one pole | *Vibrio cholerae*, *Pseudomonas* | Less common | | Lophotrichous | Tuft of flagella at one pole | *Vibrio*, *Bacillus* | Uncommon | | Amphitrichous | Flagella at both poles | *Bacillus*, *Vibrio* | Rare | **High-Yield:** In clinical microbiology, the peritrichous arrangement is diagnostically significant because it produces the characteristic "H antigen" (heat-labile) in serological typing of enterobacteria. **Clinical Pearl:** Motility testing in the laboratory (e.g., hanging drop preparation or motility agar) most commonly demonstrates peritrichous organisms, which show rapid, diffuse movement in all directions. **Mnemonic:** **PEP** = **P**eritrichous is **E**verywhere, **P**redominant ### Why Peritrichous is Most Common 1. Provides multidirectional movement capability 2. Allows rapid chemotaxis in response to environmental gradients 3. Evolutionarily advantageous for survival and nutrient acquisition 4. Predominates in Enterobacteriaceae, the most clinically relevant motile bacteria