Effect of dietary phytohaemagglutinin (PHA) on intestinal microecology and bacterial translocation in weanling rats

Normal intestinal bacteria can traverse the intestinal mucosa and enter otherwise sterile tissues by a process termed bacterial translocation. Experiments were designed to determine if dietary phytohaemagglutinin (PHA) could be used to study lectin-mediated bacterial translocation across a histologically intact intestinal epithelium. Weanling rats were fed a crude extract of Phaseolus vulgaris, a red kidney bean known to contain a high concentration of the lectin PHA. Treated rats had normal intestinal histology (light microscopy), retarded growth, intestinal bacterial overgrowth, and an increased incidence of translocation of intestinal bacteria (Escherichia coli, enterococci, and alpha-streptococci) to extraintestinal tissues. Transmission and scanning electron microscopy of intestinal segments showed dietary PHA was associated with a depletion of intestinal mucous-like material. This apparent depletion of mucous-like material was observed in animals whose intestinal goblet cells were somewhat refractory to stimulation by the secretagogue pilocarpine, as evidenced by a preponderance of undischarged mucin granules. These results suggested that the lectin binding properties of PHA might be useful in further studies designed to clarify the molecular mechanisms involved in mucus secretion and/or bacterial translocation across an intact epithelium.