[Experimental study of diarrhea induced by a strain of Escherichia coli (serogroup O-103) in growing rabbits].

The experimental infection by mouth of weaned, 6 week old rabbits was performed with Escherichia coli strain O-103/10 without any adjuvant. The quantities of E. coli for the 3 experimental treatments were - none (control) - 10(4) or 10(7) per animal. The 142 rabbits were divided into 2 groups, each including the 3 treatments: A - observation of weight and eventual diarrhea during 25 days after infection; B - killing during the same period of some healthy and diarrheic animals every 2 or 3 days, for physiological, bacteriological, and histological observations. In the A group, mortality after 25 days was 0/24 in the control, 12 and 15/24 for 10(4) and 10(7) treatments respectively, but it was observed earlier for the 10(7) one. Diarrhea has been observed for 90% of infected and 20% of control rabbits, at first on day 7, 12 and 20 post-infection for the 10(7), 10(4) and control treatments respectively. The mean duration of diarrhea was 4 days in infected and only 2 in control rabbits. Always, diarrhea and weight lost were observed before death. Although the slowing down of growth rate during the experimental period, at the end, mean live weight was quite the same for animals surviving in the 3 treatments. Necropsy of killed rabbits of the B group, revealed hemorrhagic damages mainly on cecal and colonic wall, associated with high counts for E. coli (10(7) to 8 X 10(9] in the cecal content. In rabbits with highest counts (9/15), E. coli was also observed in blood. In diarrheic rabbits cecal pH was higher (6.61 vs 5.82) and cecal VFA concentration lower (53 vs 98 mM/l) than in healthy ones; but the proportions of acetic, propionic and butyric acids were not significantly affected. At constant VFA concentration in the cecum, pH and E. coli counts were correlated (r = + 0.35). Histology revealed first, attachment of bacteria to the apex of villi cells, and furthermore destruction of the epithelium with hemorrhages and necrosis. Thus the strain O-103/10 of E. coli is confirmed to be pathogenic and will provide a good experimental model for studies of diarrhea due to E. coli.