Helicobacter pylori is a Gram-negative, spiral-shaped, microaerophilic bacterium that colonizes the human stomach.
1. **Shape and Structure:**
- **Spiral Shape:** The bacterium has a helical shape which aids in its movement through the mucus lining of the stomach.
- **Flagella:** H. pylori possesses multiple flagella, usually four to six, which allow it to be highly motile and to burrow into the gastric mucosa.
2. **Cell Wall:**
- **Gram-Negative:** It has a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides (LPS), which contribute to its pathogenicity and immune evasion.
3. **Metabolism:**
- **Microaerophilic:** H. pylori requires a low oxygen environment for optimal growth, typically around 5% oxygen.
- **Urease Production:** The bacterium produces a large amount of urease, an enzyme that breaks down urea into ammonia and carbon dioxide. This reaction neutralizes stomach acid, creating a more hospitable environment for the bacterium.
### Adaptations and Pathogenicity
1. **Acid Resistance:**
- **Urease Activity:** By producing ammonia, urease helps buffer the acidic environment of the stomach, allowing H. pylori to survive and colonize.
- **pH Homeostasis:** H. pylori maintains internal pH by regulating ion channels and using proton pumps.
2. **Adhesion Factors:**
- **BabA and SabA:** These outer membrane proteins allow H. pylori to adhere to the gastric epithelium by binding to Lewis b antigens and sialylated glycans on the host cells.
3. **Toxins and Virulence Factors:**
- **CagA:** The cytotoxin-associated gene A (CagA) protein, delivered into host cells via a type IV secretion system, disrupts cellular processes and can lead to inflammation and increased risk of gastric cancer.
- **VacA:** The vacuolating cytotoxin A (VacA) induces vacuole formation in host cells and can lead to apoptosis, immune modulation, and tissue damage.
4. **Evasion of Immune Response:**
- **LPS Variability:** Variations in LPS structure help H. pylori avoid detection by the host immune system.
- **Phase Variation and Antigenic Variation:** These mechanisms allow the bacterium to change its surface proteins and evade immune responses.
### Disease Associations
H. pylori is primarily associated with several gastrointestinal diseases, including:
- **Gastritis:** Inflammation of the stomach lining.
- **Peptic Ulcers:** Ulcers in the stomach and the first part of the small intestine (duodenum).
- **Gastric Cancer:** Chronic infection can lead to the development of gastric adenocarcinoma.
- **MALT Lymphoma:** A type of cancer affecting the mucosa-associated lymphoid tissue in the stomach.
### Diagnosis and Treatment
- **Diagnosis:** Involves urea breath tests, stool antigen tests, serology, endoscopic biopsy with rapid urease test, histology, and culture.
- **Treatment:** Typically includes a combination of antibiotics (e.g., clarithromycin, amoxicillin, metronidazole) and proton pump inhibitors to reduce stomach acid and improve antibiotic efficacy.