We analysed 106 Escherichia coli isolates, retrieved from poultry farm samples from different parts of Slovenia and isolated at the Veterinary faculty of the University of Ljubljana. In 35,85 % of isolates we confirmed the presence of conjugative plasmids that confer phenotypic resistance against ampicillin, tetracycline, cefotaxime, chloramphenicol or trimethoprim. None of the isolates was resistant against ciprofloxacin or colistin. While the majority of the conjugative plasmids were detected in isolates from air, feces and food in stalls, a lower proportion was found in isolates from flocks with high mortality due to colibacillosis. For transconjugant confirmation we used different molecular methods, including phylogenetic grouping and ERIC-PCR profiles of donors and transconjugants. Additionally, grouping of E. coli into phylogenetic groups according to the original and revised protocol was compared. Some isolates from previous group A1 thus were reassigned to group C, allowing a better distinction between donors and transconjugants. Together, 26.42 % of isolates were reassigned. The prevalence of selected virulence factor genes encoding adhesins, iron uptake systems, immune evasion factors and toxins was analysed in order to find possible links to phylogenetic group classification. Isolates with more or less virulence factor genes belonged to phylogenetic group B2 and A, respectively. Isolates from group F were predominantly retrieved from flocks with colibacillosis and have multiple virulence factors genes, including at least three iron acquisition systems. Interestingly, phylogenetic group F isolates were the only from which resistance determinants could not be transferred by conjugation.