Curli Production and ERIC-PCR Fingerprinting of Escherichia coli from Clinical Cases of Bovine Mastitis

Mastitis caused by Escherichia coli is among the most common and severe forms of environmental mastitis. Currently, the severity of E. coli mastitis is thought to be more related to cow factors than bacterial virulence. Some strains of E. coli, however, may be adapted to colonizing mammary tissue, increasing clinical severity, and impairing recovery. Curli are adhesive surface structures produced by some E. coli and Salmonella strains that bind a number of host proteins and have recently been found to play a role in the pathogenesis of bacterial sepsis. Sixty-one E. coli isolates from 36 clinical cases of bovine mastitis were characterized using ERIC-PCR and screened for their ability to produce curli by binding Congo-red dye. The effect of curli production on case recovery, based on a return to milk production, was investigated for a subset of 43 isolates from 20 quarters of 19 cows. Fifty-eight of the 61 isolates were clustered into two clonal groups at 52% genetic similarity. Thirty-five of all 61 isolates (57%) were curli-positive. Twenty-three isolates from 13 cows clustered in clonal group I, of which 5 cases (38%) were curli-positive; 35 isolates from 22 cows were clustered in clonal group II, 15 of which were curli-positive cases (68%). No association was found between genetic similarity and phenotypic curli expression of isolates from cows with clinical E. coli mastitis cases (p=0.16). Phenotypic curli expression in isolates did not affect the recovery of cows' milk yield to pre-mastitis production levels (p=0.18).