Invasive ability of Escherichia coli O18 isolated from swine neonatal diarrhea

Neonatal diarrhea occurred at two swine breeding farms in Hokkaido. Ten piglets aged 2 to 4 days were examined. Grossly, significant changes were confined to the small intestine. The mucous membrane was muddy and thickened. The intraluminal contents from the jejunum to the colon were liquid and yellow. In the small intestine, numerous Gram-negative bacilli preferentially adhered to the apex of villi. The mucosa was erosive with villous atrophy. There were bacilli also in the lamina propria and in the cytoplasm of degenerated enterocytes. Nonhemolytic Escherichia coli strains, belonging to serogroup E. coli O18 and possessing K88 fimbriae, were isolated from the small intestine. They could not be classified into any of the diarrheagenic E. coli groups because of the absence of genes of LT, STh, STp, VT1, VT2, eae, invE, and ipaH. After inoculation of the isolates on HEp-2 cells, some bacilli were engulfed by cytoplasmic projections resembling membrane ruffles and subsequently were localized in cytoplasmic vacuoles or free in the cytoplasm. These findings support the view that the present E. coli O18 is a new invasive strain enteropathogenic to piglets.