Curli production and genetic relationships among Escherichia coli from cases of bovine mastitis.

Curli are adhesive surface structures produced by some Escherichia coli and Salmonella strains that bind host proteins and activate inflammatory mediators. In this study, 61 E. coli isolates from 36 clinical cases of bovine mastitis were characterized using enterobacterial repetitive intergenic consensus-PCR and screened for their ability to produce curli. Effect of curli production on case recovery, based on a return to precase milk yield, was investigated for a subset of 43 isolates from 20 quarters of 19 cows. Thirty-five (57%) of 61 isolates were curli positive. Fifty-eight of the 61 isolates clustered into 2 clonal groups at 52% genetic similarity. Genetically diverse E. coli isolates were simultaneously cultured from individual cases. Twenty-three isolates from 13 cows were clustered in clonal group I, of which 5 cases (38%) were curli positive; 35 isolates from 22 cows were clustered in clonal group II, of which 15 cases (68%) were curli positive. No association was found between genetic similarity and phenotypic curli expression of isolates from cows with clinical E. coli mastitis cases. Phenotypic curli expression in isolates did not affect recovery of cows' milk yield to premastitis production levels.