4. Discussion
In the modern dairy industry, E. coli has frequently
emerged in cases of bovine mastitis, and this bacterium was
considered to be an environmental commensal. However,
mastitis caused by E. coli was generally a severe type .
Virulence factors and antimicrobial resistance likely played an
important role in the development of E. coli infection and
survival in these bovine hosts, and the distinctions between
the pathogenicities observed among the various strains may
have been due to the combination of virulence factors they
produced and the individual cow’s response . Phylogenetic
distribution of E. coli populations could be categorized
into groups A, B1, B2 and D; phylogenetic groups B2
and D were mainly found in extra-intestinal infections and
invasive strains, whereas groups A and B1 were mostly
associated with commensal and diarrheagenic strains . In
our study, E. coli isolates associated with mastitis mainly
belonged to groups B1 (58.6%) and A (35.7%), with only 4
(5.7%) isolates identified as group D and none as group B2.
More recently, similar reports regarding phylogenetic groups
have been published in other countries and those
findings support the role of environmental E. coli in such
cases of mastitis.