engleski

Intestinal attaching and effacing activities of porcine F4ac^+ Escherichia coli strains lacking gene for heat-labile (LT) and heat-stable (STa and STb) enterotoxins

The vaccine candidate attenuated Escherichia coli strains lacking plasmid encoding the LT and STa/STb enterotoxins were used as live whole cell bacterins. Differentiation between colonization patterns and histopathological appearance of the small intestine of pigs that have been immunized with 10^10 CFU of F4ac^+ either ETEC strain M1823 or recombinant/authentic non-ETEC strains 2407/1466, respectively, was studied in order to determine whether (or not) the fimbrial/toxin antigens produce morphologic changes in the intestinal mucosa. We also monitored the adverse effect of the oral immunization with these strains on the pig's health in a model of postweaning colibacillosis. The incidence of diarrhea, weight gain/loss rates, fecal shedding of the inoculum strain, and ultrastructural alterations in the villous epithelium of the small intestine were recorded. Pigs inoculated with strain 2407 had much lower incidence of diarrhea and the highest weight gain rate. Only pigs inoculated with 2407 had > 10^5 viable E. coli/10-cm segment of small intestine. Control and 2407-inoculated pigs (25% and 30%, respectively) gained weight substantially faster than did 1466- (7%) or M1823-inoculated pigs (10%). Ultrastructural examination of ileum from 1466- and M1823-inoculated pigs revealed moderate to severe lesions of microvilli of epithelial cells, respectively. However, the microvilli from 2407-inoculated pigs exhibited a minor structure irregularity caused by adhering E. coli cells. The results of this study indicate that different protective antigens delivered orally to pigs through vaccine candidate non-ETEC strains 1466 and 2407 can induce distinct colonization and attaching-effacing patterns in the small intestine, and hence, may produce various grades of lesions on the microvillus membranes of epithelial cells.

attaching/effacing; intestine; E. coli; pigs

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