Isolation and evaluation of the pathogenicity of a hybrid shiga toxin-producing and Enterotoxigenic Escherichia coli in pigs.

Background: Porcine pathogenic Escherichia coli (E. coli), the globally recognized important pathogen, causes significant economic loss in the field. Enterotoxigenic E. coli (ETEC) causes porcine neonatal and post-weaning diarrhea (PWD), frequently carrying F4 adhesin, F18 adhesin, Heat-Stable toxin (ST), and Heat-Labile toxin (LT). Shiga Toxin-Producing E. coli (STEC) produces F18 adhesin and Shiga toxin type 2e (stx2e), majorly leading to systemic endothelial cell damage and edema disease. In this study, hemolytic pathogenic hybrid STEC/ETEC strains carrying ST and LT genes of ETEC and the Stx2e gene of STEC isolated from pigs with PWD in Taiwan were identified. The pathogenicity of a Taiwan hybrid STEC/ETEC strain was evaluated by oral inoculation in post-weaning pigs.

Results: Next generation sequencing and multilocus sequence typing of two hybrid Taiwan porcine STEC/ETEC isolates indicated that these two isolates were closely related to the ST88 porcine hybrid STEC/ETEC isolated from pigs with watery diarrhea. Furthermore, the two hybrid Taiwan porcine STEC/ETEC isolates also displayed combinations of multiple resistance genes encoding mechanisms for target modification and antibiotic inactivation. Animal experiments confirmed that the Taiwan hybrid STEC/ETEC could cause watery diarrhea in post-weaning pigs with no signs of edema disease and minimal histopathological lesions.

Conclusion: To the best of the authors' knowledge, the present study is the first study demonstrating intestinal pathogenicity of the hybrid STEC/ETEC in pigs. The result suggests that the hybrid STEC/ETEC should be considered as a new emerging pathogen and a new target for vaccine development.