Experimental infection of post-weaned pigs with F18-encoding enterotoxigenic and enterotoxigenic/shigatoxigenic <i>Escherichia coli</i> strain isolated from the diarrheic feces in Korea

Abstract

Background: In the porcine industry, Escherichia coli (E. coli) infections have been causing post-weaning diarrhea (PWD) and edema disease (ED) for many years. It is classified into pathotypes and serotypes in animals according to virulence factors. Serotyping is performed for O, K, H, and F antigens, essential for discriminating pathogenicity and epidemiology. Furthermore, E. coli strains that produce F18 fimbriae are major sources of ED and PWD associated with  Shiga-toxin producing E. coli (STEC) expressing F18ab and enterotoxigenic E. coli (ETEC) expressing F18ac, respectively.   

Aim: To investigate the pathogenicity potential and infection characteristics of experimental infection and confirm the
pathological features of the Korean STEC/ETEC strains F18ab and F18ac in piglets.

Methods: Three-week-old pigs were  randomized into three experimental groups: infected G1 (F18ab), infected G2 (F18ac), and G3 (control). General health  status was monitored daily, and pathological changes were evaluated.

Results: Diarrhea occurred in all infected piglets.  Pathological changes were only observed in the small intestine and regional lymph nodes. In G1, mucosal necrosis,  inflammatory cell infiltration with hemorrhagic lesions, and apoptotic cell death in the tunica media of arterioles in the  small intestine were observed. In contrast, the mucosa and epithelium appeared almost intact, with no abnormal vessel  lesions in G2.

Conclusion: Both strains, isolated from pigs in Korea, could be infected and did not spread from the  alimentary tract to other organs. The pathological features were quite different among the F18 subtypes. The F18ab  strain was more virulent than F18ac, and the virulence characteristics of the F18ac strain were more similar to ETEC than  STEC.