INFECTION OF RABBIT PEYERS-PATCHES BY SHIGELLA-FLEXNERI - EFFECT OF ADHESIVE OR INVASIVE BACTERIAL PHENOTYPES ON FOLLICLE-ASSOCIATED EPITHELIUM

In order to invade the colonic mucosa, the bacterial pathogen Shigella flexneri must find a site of entry. Experiments with the rabbit ligat ed intestinal loop model described here confirm that M cells of the fo llicle-associated epithelium (FAE) that covers lymphoid structures of the Peyer's patches represent a major site of entry for invasive micro organisms. In addition, in an isogenic Shigella background, expression of an adhesive phenotype, or of an invasive phenotype, is required fo r bacteria to efficiently colonize the FAE. A nonadhesive, noninvasive mutant barely interacted with EAE. Adhesive and invasive strains indu ced dramatic but different alterations on FAE. Invasive strain M90T ca used major inflammation-mediated tissue destruction after 8 h of infec tion. Adhesive strain BS15 caused limited inflammation, but major arch itectural changes, characterized by an increase in the size of M cells that became stretched over large pockets containing an increased numb er of mononuclear cells, were observed. M cells progressively occupied large surface areas of the FAE at the expense of enterocytes. This co ntributed to enterocytes losing contact with the lumen. These experime nts demonstrate that various remodeling patterns may occur in Peyer's patches in response to bacterial pathogens, depending on the virulence phenotype expressed by the pathogenic strain.