Helicobacter pylori

Associated with antral gastritis, duodenal (peptic) ulcer, and possibly gastric ulcers and carcinomas

1. Morphology and Identification

• Spiral-shaped gram-negative rod with multiple flagella at one pole
• grows in 3-6 d at 37 ℃ in a microaerophilic environment as for C jejuni
• Skirrow's medium with vancomycin, polymyxin B, and trimethoprim, chocolate medium, other selective media with antibiotics
• A strong producer of urease -> ammonia production

2. Pathogenesis and Clinical Findings

• Grows optimally at a pH of 6.0-7.0.

How can H.pylori grow in stomach?

1) Deep in the mucus layer near the epithelial surface

On the lumen side of the mucus, the pH is low (1.0-2.0) while on the epithelial side the pH is about 7.4

2) produce Protease modifies the mucus and reduces the ability of acid to diffuse.

3) produce Urease yields production of ammonia and further buffering of acid.

• Acute infection: nause and pain, vomiting and fever, last for less than 1-2 week
• Once colonized, persists for years and perhaps decades or even a lifetime

4. Diagnostic Laboratory Tests

• Gastroscopy procedure with biopsy, Giemsa or silver stains can show the organisms.
• The sensitivity and specificity of histologic analysis approach 100%

Urease Test

• the most rapid way to detect H. pylori
• The abundance of urease produced by the organism permits detection of the alkaline byproduct in less than 2 hours: biopsy material + urea containing medium -> shift in pH -> color change
• Sensitivity: 75-95%, Specificity: 100%

5. Treatment

Triple therapy of antibiotics (metronidazole + bismuth subsalicylate or bismuth subcitrate + amoxicillin or tetracycline) + proton pump inhibitor (e.g., omeprazole) for 14 days -> eradication rate > 90% ofH. pylori and the greatest success in curing gastitis or peptic ulcer disease

6. Epidemiology & Control

• Infections are common, particularly in people in a low socioeconomic class or in developing nations
• <> 80% in adults
• Humans are the primary reservoir, an animal reservoir has not been identified
• person-to-person transmission (fecal to oral)

Category: Microbiology Notes