Which of the following is the characteristic morphology of Campylobacter jejuni on Gram staining?

Explanation

## Morphology of Campylobacter jejuni **Key Point:** Campylobacter jejuni is a Gram-negative, microaerophilic bacterium with a distinctive comma or S-shaped (curved rod) morphology on Gram staining. ### Identifying Features - **Shape:** Comma-shaped or S-shaped curved rods (not spiral) - **Gram staining:** Gram-negative - **Size:** 0.2–0.8 μm × 1.5–3.5 μm - **Motility:** Highly motile with unipolar or bipolar flagella (darting motility) ### Distinguishing from Helicobacter pylori | Feature | Campylobacter jejuni | Helicobacter pylori | |---------|----------------------|---------------------| | Morphology | Comma/S-shaped | Spiral (4–6 turns) | | Flagella | Unipolar/bipolar | Lophotrichous (multiple) | | Habitat | Intestinal tract | Gastric mucosa | | Culture medium | Campy agar (selective) | Selective media with antibiotics | **High-Yield:** The comma shape is so characteristic that it is often used for presumptive identification in clinical microbiology labs. The spiral morphology is specific to *Helicobacter pylori*, not *Campylobacter*. **Clinical Pearl:** Campylobacter jejuni is the most common bacterial cause of acute diarrhea in developed countries, especially in children and young adults.