Helicobacter pylori

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Helicobacter pylori
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Helicobacter spp

• Helical, curved-or-straight, Gram negative rods
• Darting motility
• May appear coccoid in stationary phase
• Microaerophilic, grow optimally at 37C
• Hydrogen may be required for growth
• Infections widely-documented in mammals and birds
• zoonotic
• cause gastritis, gastric cancer, hepatitis,
  hepatic cancer, and gastroenteritis

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H. pylori Virulence Factors

• cagA encodes CagA protein (some strains)
• infection with cagA strains higher risk of
  ulcers, stomach cancer
• part of chromosomal region containing genes for
  type IV secretion system
• export molecules into host cells
• CagA enters epithelial cell, interacts with human
  proteins
• Affects cell shape, secretions, signalling
• cagA strains cause more severe inflammation,
  tissue injury than non-cagA strains
• May explain increased disease risk in people
  carrying cagA strains

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H. pylori Virulence Factors

• VacA encoded by vacA
• gene present in every strain, few make functional
  toxin (variable genotypes)
• vacuolation in cultured cells
• compromises white blood cell function in stomach,
  diminishes immune response
• Urease
• acts on urea
• produces cloud of ammonia around organism
• lowers pH, facilitates colonization
• Strains bearing specific vacA genotype and cagA
  associated with highest risk of stomach cancer
• Host factors can increase risk

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• Nearly all adults in developing world carry
  organism
• 70- 100 of children infected by age 10
• colonized for life
• Prevalence much lower in developed countries
• lt 10 of US-born children carry organism
• improved hygiene, widespread use of antibiotics

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• GOOD NEWS
• incidence of peptic ulcer disease, stomach cancer
  declining in developed countries
• 1900 stomach cancer was leading cause of cancer
  death in U.S
• 2000 incidence, mortality rate lt 20
• BAD NEWS
• rise in incidence of esophageal diseases
• increased esophageal adenocarcinoma
• aggressive cancer in distal esophageal lining
• fastest-increasing major cancer in US
• 5 year survival rate lt 10

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