Molecular characterization of Diarrheagenic Escherichia coli strains Isolated from Dairy Calves in North Shoa Zone, Oromiya Region, Ethiopia

Background Diarrheagenic E. coli (DEC) strains are associated with several outbreaks and sporadic cases worldwide. Understanding the nature of the organisms is important in order to tailor preventive and control strategies before any harm emanates. Methods In this study a total of 73 E. coli isolates from diarrheic dairy calves found in 56 farms located in North Shoa Zone, Oromiya Region, were characterized based on their virulence genes and plasmid profile. Moreover, the study showed the relationship between virulence genes, plasmid profile and antibiotic resistance traits were assessed. Results Virulence genes (VGs) were detected in 69.86% of isolates, carrying at least one of the six VGs screened. Among the VGs eae was most frequent, observed in 58.90% of isolates, followed by stx1 , 34.25%, stx2 , 24.66%, ehlyA , 23.29%, bfpA , 12.33% and aatA , 5.48%. A total of eleven distinct virulence profiles were identified based on combination of virulence genes and isolates were placed into five different pathotypes with a frequency of EHEC, 30%, tEPEC, 12%, aEPEC, 16%, and STEC and EAEC, 6% each. Plasmid analysis revealed the occurrence of ten different kinds of plasmids ranging in size from 2.6 + 0.14 Kbp to 98.2 + 4.17 Kbp and exhibited 13 different kinds of profiles among the isolates. A significant one to one correlation was observed among virulence factors, plasmid content and antibiotic resistance traits with a Pearson product moment correlation in a range of r = 0.17 to r = 0.56. Accounting to the total dataset, isolates showed significant segregation in to the sample site, indicating spatial clustering of isolates based on overall pathogenic characteristics. Conclusions The demonstration of pathogenic potential in substantial amount of E. coli isolates from dairy farms from all the three sites indicates the level of risk posed in humans as well as animals. Thus, identifying potential sources and route of transmission of DEC is vitally important in order to establish control and prevention strategies for diarheagenic E. coli infection.