HISTOPATHOLOGICAL FEATURES IN THE SMALL-INTESTINE OF PIGS INFECTED WITH F4AC(-ENTEROTOXIGENIC OR ENTEROTOXIGENIC STRAINS OF ESCHERICHIA-COLI() NON)

Four porcine strains of Escherichia coli were examined for their effec ts on the small intestine of 4-week-old weaned pigs infected orogastri cally. The strains used experimentally were: strain 1467 (adhesin nega tive, non-toxigenic); strains 2407 and 1466 (adhesin positive, non-tox igenic), derived by genetical engineering from strain 1467 and contain ing a wild type plasmid and a recombinant plasmid, respectively, encod ing the F4 antigen (adhesin); and strain M1823 (adhesin positive, toxi genic). In addition, 2-week-old pigs that died from natural colibacill osis associated with two strains (''Ihan 1 and 2''; adhesin positive, toxigenic) were examined. Strain M1823 and the Ihan strains produced m oderate and marked lesions, respectively. Strain 1467 did not cause mu cosal damage or an inflammatory response. Strains 1466 and 2407 caused a mild to moderate leucocyte (mononuclear and polymorphonuclear) infi ltration in the jejunal (but not ileal) lamina propria. However, unlik e strain 1466, strain 2407 did not cause damage to the small intestina l mucosa and should be further studied as a potential oral vaccine str ain for post-weaning E. coli diarrhoea.