Internalization of multiple bacterial strains into the gut mucosa during the post-infective phase. (A) Representative photomicrographs of bacterial internalization into the post-infective gut mucosa (magnification ×200). Jejunal segments of Giardia-infected mice and saline controls were subjected to FISH with universal bacterial DNA probes. Bacteria (green, top panel) were detected in the epithelial layer and lamina propria of Giardia-infected mice but not in saline controls. A higher magnification of mucosal bacteria is shown in the insets. Hoechst-stained cell nuclei (blue, bottom panel) are shown for orientation. Photoimages were obtained from at least four mice per group. (B) Classification of internalized bacterial strains in the post-infective phase. Bacterial colonies cultured from lysed mucosal cells of jejunal (N = 196) and colonic (N = 133) segments were subjected to Gram staining. The percentages of colonies classified as Gram-positive or -negative rods or cocci are shown.