Sisay, Tesfaye (PhD)Endale, Abinet2019-05-082023-11-182019-05-082023-11-182018-06-03http://etd.aau.edu.et/handle/12345678/18210Diarrheagenic 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. Thus, the distribution of these organisms among humans as well as animals should be studied, which was the major objective of the current study. In this study a total of 73 E. coli samples isolated from feces of dairy calves found in 56 farms located in Fiche, Debretsige and Muketuri areas were characterized. Isolates were assessed and characterized based on their virulence gene and plasmid content. Moreover, the study tried to show the relationship between virulence gene, plasmid content antibiotic resistance traits. The study identified the occurrence of virulence genes 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% observed in the total sample isolates. 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 6% of STEC and EAEC each. Plasmid analysis on the other hand 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 distribution profile among isolates. In an effort made to observe any possible association among virulence factors, plasmid content and antibiotic resistance traits, a significant one to one correlation was observed. 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. The demonstration of pathogenic potential in substantial amount of E. coli isolates from dairy farms from all the three sites indicate 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 DEC infection. Moreover, nationwide screening for virulence factors and antibiotic resistance genes and associated plasmids is recommended in order to prevent the spread of these pathogens among various sources.enCalfDiarrheaEscherichia ColiPlasmidVirulence FactorVirulence GeneThesis