O-Serogroups and Pathovirotypes of Escherichia coli Isolated from Post-Weaning Piglets Showing Diarrhoea and/or Oedema in South Korea

This study aimed to determine the prevalence of several pathovirotypes and evaluate the association of haemolysis with the virotypes of pathogenic E. coli isolated from post-weaning piglets in South Korea from 2015 to 2019. We isolated 890 E. coli and tested for O-serogroups, virulence genes, haemolysis, and multilocus sequence typing. The predominant virotypes were STb:EAST1:AIDA-I, F18b:Stx2e:AIDA-I, F18:STa:STb:Stx2e, and eae:Paa in enterotoxigenic E. coli (ETEC), Shiga toxin-producing E. coli (STEC), ETEC/STEC, and enteropathogenic E. coli (EPEC), respectively. Regarding serogroups, O139, O149, O141, and O121 were mostly detected in F18:Stx2e:AIDA-I, F4:LT:STb:EAST1, F18:STa:STb, and F18:Stx2e:EAST1, respectively. There was a significant change in the frequency of the O141:F18ac:STa:STb (an increase from 1.6% to 10.1%) and O139:F18ab:Stx2e:AIDA-I (a decrease from 13.0% to 5.3%) virotypes in ETEC and STEC, respectively, from 2015 to 2019. The O141:F18ac:STa:STb virotype was mostly detected in the central area and was spreading to the southern area. The odds ratios between haemolysis and virotypes were 11.0, 6.25, and 8.57 in F18:STa:STb, F18:Stx2e:AIDA-I, and F4:LT:STb:EAST1, respectively. Our findings provide insights regarding the recent prevalence of pathogenic E. coli in South Korea and could be used for the development of vaccines for E. coli responsible for PWD and ED in post-weaning piglets.