Résumé
Escherichia coli [E. coli] is the predominant coliform species causing intramammary infections. Where in the present study, E. coll isolates were 1.8 strains [17.82%] followed by Enterobacter aerogenes 3 strains [2.97%] and Klebsiella pneumoniae one strain [0.99%] from 101 clinical mastitic milk samples of cows. Eighteen E. coli isolates were serotyped to nine different serogroups; O111:H4 [3], O127:H6 [3], O26 [2], O126 [2], O119:H6 [1], O114:H21 [1], O55:H7 [1], O44:H18 [1], O124[1] and [3] untyped. Virulence tests were performed on the 18 isolated E. coll, it was found that 15 isolates [83.3%] were serum resistant, 13 isolates [72.2%] had Congo Red binding activity, 6 isolates [33.3%] were invasive and one isolate [5.6%] had haemolytic activity. PCR was applied to detect the presence of Shiga like toxin producing E. coll [stxl and stx2 genes] on the nine different strains[one strain for each serogroup], where stxl and stx2 were found in 8 [88.9%] and 4 [44.4%] of the nine examined strains, respectively. While stxl and stx2 genes were found together in 3 strains [33.3%]. Conclusions: E. coli isolates usually posses one or more virulence factors that may help in establishment at the infection site and subsequently causing clinical bovine mastitis