Helicobacter pylori Flashcards
Helicobacter pylori
Gram-negative, highly motile, spiral-shaped bacterium
Colonizes the non-acid-secreting mucosa of the stomach and the upper intestinal tract
Associated with gastritis, ulcers & gastric cancers
Prevalence of colonization ranges from 20% in developed countries to more than 90% in the developing world
Approx. 10% will develop peptic ulcers, 1-3% gastric cancer & 0.1% MALT lymphoma
Helicobacter pylori & peptic ulcers
The gastric mucus layer protects H. pylori from stomach acid
A combination of H. pylori products and host responses cause inflammation, tissue destruction & ulceration
Such peptic ulcers traditionally treated with long-term antacids, only with partial success (typically relapsing within 1 year)
Discovery of association with H. pylori revolutionised treatment and led to awarding of Nobel Prize in 2005
Ulcers now effectively treated with a 14-day course of antibiotics
Helicobacter pylori & carcinogenesis
Some H. pylori isolates carry the cag pathogenicity island (cag PAI) (pathogenicity islands are part of the genome that encodes factors associated with pathogenicity)
The cag PAI encodes the CagA protein (Cytotoxin-associated gene A) and the Cag type IV secretion system (SM lectures). Hollow needle injects effectors into the host cell
Patients harbouring cag+ strains are at heightened risk of gastric cancer
CagA is injected into host cell by the type IV secretion system, whereupon it interacts with numerous host cell proteins. In doing so, it activates downstream signalling pathways and enhances the proliferative ability of the gastric epithelial cells.
Helicobacter pylori & gastric MALT lymphomas
H. pylori can also be associated with gastric MALT lymphomas (blood cancer)
MALT, mucosa-associated lymphoid tissue; part of the normal response to infection at mucosal sites
The inflammation associated with chronic H. pylori infection/colonisation can be associated with development of gastric MALT lymphoma
Constant stimulation of lymphocytes recruited to the infection can promote mutations in the lymphocytes, resulting in lymphomas (uncontrolled lymphocyte proliferation)
The pros & cons of targeting Helicobacter pylori
Association of H. pylori with ulcers and cancers has led to investigation of strategies to eradicate H. pylori (antibiotics &/or vaccination)
However, H. pylori has also been associated with beneficial effects, with a decreased risk of:
Reflux oesophagitis
Childhood-onset asthma
Obesity
The potential implications of altering microbiota composition can be wide-ranging and need to be fully assessed
Oesophagitis is an inflammation of the lining of the oesophagus (gullet), usually caused by the digestive juices in the stomach repeatedly moving upwards into the lower oesophagus (reflux).
