Pathogenic Mechanisms of Helicobacter pylori: Production of Cytotoxin

Abstract

Bacteria associated with mucosal infections of the digestive system generally produce toxins, especially when they cause inflammatory lesions. Illnesses due to thermotolerant campylobacters, to enterohemorrhagic Escherichia coli, and to Clostridium difficileare only some examples. It would be surprising if Helicobacter pylori (HP) did not produce any toxic substances. The difficulty consists in attributing a pathogenic meaning to the toxin, since the range is quite wide of clinical and histological presentation of gastroduodenal inflammatory diseases linked to the presence in the stomach of H. pylori organisms [1]. Johnson and Lior [2] firstly reported the production of heat-labile cytotoxin by 80.6% of 36 HP strains they tested. However, most of our knowledge of the cytotoxigenicity of HP is from Leunk et al. [3] whose work has inspired us in part. They found that about 55% of 201 HP strains isolated in four different parts of the world produced a substance which caused intracellular vacuolization in cells of several lines in vitro, not only in lines generally employed in toxigenicity tests, like Chinese hamster ovary (CHO) cells, Vero cells, and Y-1 cells, but also in human tumoral cells like HeLa, KATO III, and HEp-2, as well as in human embryonic intestinal cells which were the most responsive. They also inferred that the toxin was proteinaceous in nature being heat labile (destroyed at 70 °C for 30 min), protease sensitive, and ammonium-sulfate precipitable. Its molecular weight ought to be higher than 100 kDa since cytotoxic activity could be found only in the retentate of a concentrated broth culture filtrate (CBCF) passed through 100 kDa molecular weight limit ultrafiltration membrane.