Phylogenetic group, virulence factors and antimicrobial resistance of Escherichia coli associated with bovine mastitis.

Escherichia coli is an important pathogen involved in the etiology of bovine mastitis. A total of 70 E. coli isolates recovered from clinical and subclinical mastitis samples were characterized with respect to their phylogenic group, virulence factors and antimicrobial susceptibility. Based on the presence of the specific genes chuA, yjaA and TspE4.C2, these isolates were found to belong to three different groups: group A(25), group B1(41) and group D(4). Twenty-five (35.7%) isolates harbored at least one virulence gene, and the most prevalent virulence genes were f17A, irp2, astA, iucD and colV. The irp2-coding gene was more often detected in group A than in group B1 isolates; in contrast, colV was identified more often in group B1 isolates. The majority of isolates (87.1%) were resistant to at least one antimicrobial compound. Forty-seven isolates (67.1%) were resistant to streptomycin, and those from group B1 were more resistant to streptomycin than isolates from group A. The latter feature was supported by the distribution of streptomycin resistance genes observed in group B1 compared to group A.