COMPREHENSIVE STUDY OF THE INTESTINAL STAGE OF LISTERIOSIS IN A RAT LIGATED ILEAL LOOP SYSTEM

The intestinal stage of listeriosis was studied in a rat ligated ileal loop system. Listeria monocytogenes translocated to deep organs,vith similar efficiencies after inoculation of loops with or without Peyer' s patches. Bacterial seeding of deep organs was demonstrated as early as 15 min after inoculation, It was dose dependent and nonspecific, as the Delta inlAB, the Delta hly, and the Delta actA L. monocytogenes m utants and the nonpathogenic species, Listeria innocua, translocated s imilarly to wild-type L, monocytogenes strains, The levels of uptake o f listeriae by Peyer's patches and villous intestine were similar and low, 50 to 250 CFU per cm(2) of tissue. No listeria cells crossing the epithelial sheet of Peyer's patches and villous intestine were observ ed by transmission electron microscopy, The lack of significant intera ction of listeriae and the follicle-associated epithelium of Peyer's p atches was confirmed by scanning electron microscopy. The follicular t issue of Peyer's patches was a preferential site of Listeria replicati on. With all doses tested, the rate of bacterial growth was 10 to 20 t imes higher in Peyer's patches than in villous intestine, At early sta ges of Peyer's patch infection, listeriae were observed inside mononuc lear cells of the dome area. Listeriae then disseminated throughout th e follicular tissue except for the germinal center. The virulence dete rminants hly and, to a lesser extent, actA, but not inlAB, were requir ed for the completion of this process, This study suggests that Peyer' s patches are preferential sites for replication rather than for entry of L. monocytogenes, due to the presence of highly permissive mononuc lear cells whose nature remains to be defined.