A 32-year-old man from rural India presents with acute watery diarrhea and cramping abdominal pain for 3 days. Stool culture on Campy food agar at 42°C yields oxidase-positive, gram-negative curved rods. A second patient with chronic epigastric pain and dyspepsia shows a positive rapid urease test on gastric antral biopsy. Which finding best differentiates the first organism from the second?

Explanation

## Clinical Differentiation: Campylobacter jejuni vs. Helicobacter pylori ### Case Analysis **Patient 1:** Acute diarrhea + Campy food agar growth at 42°C + oxidase-positive curved rods = **Campylobacter jejuni** **Patient 2:** Chronic dyspepsia + positive urease test on gastric biopsy = **Helicobacter pylori** ### Key Discriminating Feature: Temperature Optimum | Property | Campylobacter jejuni | Helicobacter pylori | |----------|----------------------|---------------------| | **Optimal growth temperature** | **42–43°C** | **37°C** | | **Growth at 37°C** | Poor/minimal | Excellent | | **Growth at 42°C** | Excellent (selective) | Inhibited | | **Oxidase test** | Positive | Positive | | **Urease test** | Negative | Positive | | **Gram stain** | Gram-negative | Gram-negative | | **LPS in cell wall** | Yes | Yes | **High-Yield:** The **42°C selective growth** is the single most practical laboratory discriminator. Campylobacter's thermophilic preference is exploited in culture media (Campy food agar incubated at 42°C inhibits most normal flora). H. pylori cannot tolerate 42°C and requires 37°C. ### Why Temperature Matters **Clinical Pearl:** Campylobacter jejuni colonizes the small intestine of warm-blooded animals (chickens, cattle) where body temperature is 40–42°C. This thermophilic trait is an evolutionary adaptation to its ecological niche. H. pylori, adapted to the human stomach (37°C), is mesophilic. **Mnemonic:** **42 = C**ampylobacter's **C**omfort zone. **37 = H**elicobacter's **H**ome temperature. ### Why Other Options Fail - **Oxidase & Gram-negative:** Both organisms are oxidase-positive and gram-negative — shared traits, not discriminators. - **LPS in cell wall:** Both gram-negative bacteria possess LPS — not distinctive. - **Urease test:** While H. pylori is urease-positive and Campylobacter is urease-negative, this is a biochemical enzyme assay, not a structural or growth-based discriminator. The question emphasizes *findings* from the clinical vignette; the first patient's culture result (42°C growth) is the most direct discriminator. [cite:Textbook of Microbiology Ananthanarayan 10e Ch 45; Harrison 21e Ch 155]