A 28-year-old man from rural Maharashtra presents with a 5-day history of crampy abdominal pain and bloody diarrhea. He reports consuming undercooked chicken at a wedding 3 days prior. On examination, he is afebrile with mild abdominal tenderness. Stool microscopy shows motile, curved gram-negative rods. Culture on selective media (Campy food agar at 42°C, microaerophilic conditions) yields oxidase-positive colonies. Which is the most likely organism and its key virulence mechanism?

Explanation

## Diagnosis: Campylobacter jejuni Gastroenteritis ### Clinical Features & Epidemiology **Key Point:** Campylobacter jejuni is the most common bacterial cause of acute diarrhea worldwide, particularly in resource-limited settings. Poultry and undercooked poultry products are the primary reservoir. ### Microbiological Identification | Feature | Campylobacter jejuni | |---------|---------------------| | **Morphology** | Curved, S-shaped or spiral gram-negative rod | | **Motility** | Highly motile (characteristic "darting" motion in wet mount) | | **Culture conditions** | Microaerophilic (5% O₂, 10% CO₂); optimal temp 42°C | | **Selective media** | Campy food agar, mCCDA (with antibiotics to suppress normal flora) | | **Oxidase test** | Positive | | **Catalase test** | Positive | **High-Yield:** The combination of curved morphology, microaerophilic growth at 42°C, oxidase positivity, and isolation from poultry-contaminated food is pathognomonic for C. jejuni. ### Virulence Mechanisms 1. **Cytolethal Distending Toxin (CDT)** — the primary virulence factor - Causes DNA double-strand breaks in epithelial cells - Leads to cell cycle arrest and apoptosis - Responsible for mucosal inflammation and bloody diarrhea 2. **Invasion & Translocation** - Invades intestinal epithelium via M cells in Peyer's patches - Triggers inflammatory response with neutrophil infiltration - Results in hemorrhagic colitis 3. **Lipopolysaccharide (LPS)** - Gram-negative endotoxin contributing to systemic inflammation ### Clinical Presentation **Key Point:** Campylobacteriosis typically presents as acute inflammatory diarrhea (often bloody) with crampy abdominal pain, fever, and malaise. Symptoms usually resolve within 7–10 days with supportive care. **Clinical Pearl:** Post-infectious complications include reactive arthritis (HLA-B27 association) and Guillain-Barré syndrome (GBS), which can occur 2–3 weeks after diarrheal illness due to molecular mimicry between bacterial lipooligosaccharides and peripheral nerve myelin. ### Management - Most cases are self-limited; supportive care (oral rehydration) is the mainstay - Antibiotics (azithromycin or fluoroquinolone) indicated for severe disease, immunocompromised patients, or systemic involvement - Avoid antimotility agents (risk of toxic megacolon) **Mnemonic:** CAMP = **C**urved rod, **A**erophilic (micro), **M**otile, **P**oultry source