Characterization of virulence genes in Escherichia coli strains isolated from pre-weaned calves in the Republic of Korea

Background Escherichia coli is an important cause of diarrhea in calves and its diarrheagenic properties are related to presence of certain virulence genes. In this study, the prevalence of virulence genes F5, F17, F41, sta, stx1, stx2, eae, and saa in E. coli isolated from pre-weaned calves presenting with (n= 329) or without diarrhea (n= 360) was explored using multiplex polymerase chain reaction. We also evaluated the association between detection of E. coli and the presence of diarrhea. Results Escherichia coli was detected in 56.3% (388/689) of the fecal samples and showed the highest prevalence (66.5%) in 21-40-day-old calves and the lowest (46.3%) among those that were 1-20 days old. The prevalence of the enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC) pathotypes was detected in 73.9% and 15.9%, respectively. The results showed no association between diarrhea and the presence of E. coli in general, ETEC or STEC. The F17 gene was the most frequently detected virulence factor in E. coli of calves of all ages regardless of diarrhea. Interestingly, the results show that the calves aged 41-60 days with F17-positive E. coli are at a higher risk for production of Shiga toxin (Stx1; 95% confidence intervals: 1.86-31.95; P = 0.005) compared to calves aged 1-20 days; no association between this finding and diarrhea was observed among the calves of this age group. Moreover, the virulence genes associated with the ETEC and STEC strains were not significantly associated with pathogenicity in this study cohort. Conclusions These results suggest that while the incidence of E. coli is age-related, there was no relationship linking E. coli virulence genes to calf age and diarrhea. Furthermore, the present study demonstrated that detection of E. coli strains either with or without virulence factors was not associated with diarrhea in pre-weaned calves. Keywords: Diarrhea, ETEC, F17, STEC, Pre-weaned calves, Virulence genes