Microbiology · Other Gram-negative rods
Helicobacter pylori !
- Bacterium
- Gram-negative
- Exam priority: high
A bacterium that lives in the stomach, usually from childhood. It causes gastritis and ulcers and raises the risk of stomach cancer.
Updated 2026-11-01
At a glance
- Gram
- Gram-negative
- Shape
- Curved or spiral rod with flagella
- Oxygen
- Microaerophilic
- Family
- Helicobacteraceae
- Stain
- Gram: curved red rods; in biopsies, Giemsa or silver
Morphology
- Curved Gram-negative rod with several flagella at one end
- Urease-, catalase- and oxidase-positive
- Lives under the mucus layer of the gastric antrum
Transmission
- Person to person by oral-oral or fecal-oral routes, mostly in childhood and within families
- Contaminated water and food are possible sources
Reservoir: Human stomach
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Urease: makes ammonia that neutralizes the acid around it and injures the mucosa
- Flagella: swim through gastric mucus
- Adhesins: attach to the epithelium
- CagA and VacA: strong inflammation, cell damage and higher ulcer and cancer risk
Diseases it causes
- Chronic gastritis, mainly of the antrum Helicobacter pylori gastritis →
- Duodenal and gastric peptic ulcer Peptic ulcer disease →
- Gastric adenocarcinoma (group 1 carcinogen) Gastric cancer →
- Gastric MALT lymphoma, which can regress after eradication
Clinical picture
- Most infected people have no symptoms
- Burning epigastric pain, often on an empty stomach
- Alarm signs: GI bleeding, weight loss, anemia, persistent vomiting
Diagnosis
- Urea breath test and stool antigen: detect active infection
- Endoscopy with biopsy: rapid urease test, histology and culture
- Serology cannot tell current from past infection
- Recent proton pump inhibitors, bismuth or antibiotics can give false negatives
- Eradication is confirmed after treatment
Treatment
A proton pump inhibitor combined with antibiotics: bismuth quadruple therapy (bismuth, metronidazole and tetracycline) where clarithromycin resistance is high, or amoxicillin-clarithromycin therapy where it is low. Resistance to clarithromycin and metronidazole is the main reason treatment fails.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
- Proton pump inhibitors (PPIs)
- Omeprazole
- Amoxicillin
- Clarithromycin
- Metronidazole
- Bismuth subsalicylate
- Tetracycline
Prevention
- Safe water, handwashing and well-prepared food
- No vaccine
- Testing and eradication are considered in families with gastric cancer
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme lets H. pylori survive in the stomach, and which test uses it?
Urease, which makes ammonia; it is used in the urea breath test and the rapid urease test on biopsies.
Which cancers are linked to H. pylori infection?
Gastric adenocarcinoma and gastric MALT lymphoma.
Why is serology useless to confirm eradication?
Antibodies persist long after the bacterium is gone.
What does bismuth quadruple therapy contain?
A proton pump inhibitor, bismuth, metronidazole and tetracycline.
Related
Related conditions
← Back to the group: Other Gram-negative rods
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Helicobacter pylori Infection (MSD Manual Professional Edition, 2025); Helicobacter pylori Infections (MedlinePlus, 2025).
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Representative model, for educational purposes only.