{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Helicobacter pylori is a Gram-negative, microaerophilic (requires oxygen, but at a lower concentration than is found in the atmosphere) bacterium found in the stomach, and may be present in other parts of the body, such as the eye. Helicobacter pylori is a helix-shaped bacterium about 3 μm long with a diameter of about 0.5 μm. Strains of Helicobacter pylori produce high levels of two proteins, vacuolating toxin A (VacA) and the cytotoxin-associated gene A (CagA), appear to cause greater tissue damage than those that produce lower levels or that lack those genes completely. These proteins are directly toxic to cells lining the stomach and signal strongly to the immune system that an invasion is underway. This antibody reacts with Helicobacter pylori on the surface of epithelial cells of infected specimens."}]}]}