BACTEROIDES-FRAGILIS ENTEROTOXIN MODULATES EPITHELIAL PERMEABILITY AND BACTERIAL INTERNALIZATION BY HT-29 ENTEROCYTES

Background & Aims: Enterotoxigenic Bacteroides fragilis has been assoc iated with diarrheal disease, and the enterotoxin has a cytopathic eff ect on cultured HT-29 enterocytes, Experiments were designed to determ ine the effect of B. fragilis enterotoxin on bacteria-enterocyte inter actions, Methods: Confluent HT-29 enterocytes were incubated for 1 hou r with B. fragilis enterotoxin, followed by 1 hour of incubation with pure cultures of enteric bacteria, namely, Salmonella typhimurium (two strains), Listeria monocytogenes (three strains), Proteus mirabilis, Escherichia coli (three strains), and Enterococcus faecalis, Enterocyt e viability was assessed using vital dyes, epithelial permeability was measured using transepithelial electrical resistance, enterocyte morp hology and bacteria-enterocyte interactions were visualized using ligh t and electron microscopy, and bacterial internalization was assessed using a quantitative culture of lysed enterocytes. Results: B. fragili s enterotoxin did not affect enterocyte viability but decreased transe pithelial electrical resistance, and individual enterocytes pulled apa rt, Enterotoxin pretreatment decreased internalization of L. monocytog enes (P < 0.01) but increased (P < 0.01) internalization of the other strains of enteric bacteria, Augmented bacterial internalization was a ssociated with preferential bacterial adherence on the exposed lateral surface of enterotoxin-treated enterocytes. Conclusions: B. fragilis enterotoxin was associated with HT-29 cell rounding and with augmented internalization of selected strains of enteric bacteria that were pre ferentially adherent on the exposed enterocyte lateral surface.