Proteins of tight junctions provide the targets or certain common bacteria of medical importance. The enterotoxin肠毒素 secreted by Clostridium perfringens产气荚膜梭菌, which causes “ food poisoning,” binds claudin molecules of intestinal cells, prevents insertion of these proteins during maintenance of tight junctions, and causes loss of tissue fluid into the intestinal lumen via the paracellular pathway. Similarly, Helicobacter pylori幽门螺杆菌, which is important in the etiology of gastric ulcers, binds the extracellular domains of tight-junction proteins in cells of the stomach and inserts a protein into these cells, which targets ZO-1 and disrupts signaling from the junction.

阅读短文，思考产气荚膜梭菌和幽门螺杆菌的致病机理及其与紧密连接之间的关系。