A 32-year-old man from rural India presents with a 3-week history of bloody diarrhea, abdominal cramps, and fever. Stool culture on selective media (Campy food agar) grows oxidase-positive, curved gram-negative rods. Which investigation is most appropriate to confirm the organism as Campylobacter jejuni?

Explanation

## Confirmatory Test for Campylobacter jejuni **Key Point:** Hippurate hydrolysis is the single most specific biochemical test to differentiate *Campylobacter jejuni* from other Campylobacter species. ### Why Hippurate Hydrolysis? *Campylobacter jejuni* possesses the enzyme hippuricase, which hydrolyzes hippuric acid (N-benzoylglycine) to benzoic acid and glycine. This test is: - **Highly specific** for C. jejuni (90–95% positive) - **Rapid** — result in 2–4 hours - **Differentiates** C. jejuni from C. coli (negative) and other species ### Diagnostic Algorithm for Campylobacter ```mermaid flowchart TD A[Curved, gram-negative rod<br/>Oxidase-positive<br/>Thermophilic]:::outcome --> B{Hippurate<br/>hydrolysis?}:::decision B -->|Positive| C[Campylobacter jejuni]:::outcome B -->|Negative| D{Indole<br/>production?}:::decision D -->|Positive| E[Campylobacter coli]:::outcome D -->|Negative| F[Other Campylobacter spp.]:::outcome ``` ### Other Biochemical Tests (Not Useful Here) | Test | C. jejuni | C. coli | Clinical Use | |------|-----------|---------|---------------| | Urease | Negative | Negative | Not discriminatory | | Methyl red | Negative | Negative | Not discriminatory | | Indole | Negative | Positive | Differentiates C. coli | **High-Yield:** Urease test is positive in *Helicobacter pylori*, not Campylobacter — a common exam trap. ### Clinical Pearl *Campylobacter jejuni* is the most common bacterial cause of acute gastroenteritis in developed countries and is increasingly recognized in India. Thermophilic growth (42°C) and oxidase positivity are presumptive; hippurate hydrolysis confirms the species. [cite:Park 26e Ch 3]