Helicobacter pylori
One-Sentence Definition
Helicobacter pylori is a microaerophilic, urease-positive curved Gram-negative bacillus that colonizes the human stomach and drives gastritis, peptic ulcer disease, and risk of gastric adenocarcinoma and MALT lymphoma.
Taxonomy & Morphology
- Campylobacterales; spiral/curved rods; multiple polar flagella
- Oxidase-, catalase-, and urease-positive (survives acid via NH₃ from urea)
- Strictly associated with gastric mucosa in humans (person-to-person / family clustering)
Virulence Highlights
- Urease — acid resistance
- CagA (cag PAI — a genomic island) — injected via T4SS; associated with ulcer/cancer risk
- VacA — vacuolating cytotoxin; allele variants modulate virulence
- Motility and adhesins for mucus/epithelial niche
Clinical Syndromes
- Chronic gastritis (nearly universal if colonized)
- Duodenal/gastric ulcers
- Increased risk gastric adenocarcinoma; MALT lymphoma (may regress with eradication)
- Dyspepsia workups — test-and-treat strategies in selected populations
Diagnosis
- Noninvasive: urea breath test, stool antigen
- Invasive: biopsy urease, histology, culture (for AST when refractory)
- Serology: marks exposure; poor for test-of-cure
- Molecular detection / resistance PCR on stool or biopsy increasingly used
Treatment Notes (conceptual)
- Multi-drug eradication regimens (PPI + antibiotics); local resistance guides empiric choice
- Confirm eradication after therapy when clinically indicated
- Avoid endless empiric courses without testing — stewardship + guideline adherence
AMR
- Clarithromycin resistance (23S rRNA mutations) — major empiric-regimen failure driver
- Metronidazole, levofloxacin, amoxicillin, rifabutin resistance patterns vary geographically
- Culture/AST or molecular resistance testing for refractory disease
Genomics & Computational Notes
- High within-host diversity; recombination; multilocus / WGS for phylogeography
- cag PAI presence/absence and VacA genotyping for research risk stratification
- Example of chronic colonization + cancer association in bacterial pathogenesis teaching
Related Notes
- Campylobacter jejuni (related order) · Gastrointestinal Infections · Antimicrobial Stewardship
- MOCs: MOC - Bacteriology · MOC - Clinical Microbiology · MOC - Antimicrobial Resistance (AMR)
Active Recall
- How does urease allow gastric survival?
- What is CagA’s delivery system, and why does it matter clinically?
- Why is serology a poor test-of-cure?