J. Dairy Sci. 89:3408–3412 © American Dairy Science Association, 2006. Escherichia coli Isolates ’ Serotypes, Genotypes, and Virulence Genes and Clinical Coliform Mastitis Severity

Dairy cattle with clinical mastitis caused by Esche-richia coli exhibit a wide range of disease severity, from mild, with only local inflammatory changes of themam-mary gland, to severe, with significant systemic de-rangement. The present study was designed to examine the relationship between serotype and virulence genes of E. coli mastitis isolates, different levels of systemic disease severity, and farm from which the E. coli strain was obtained. One hundred twenty-three E. coli milk isolates were obtained from cows with clinical mastitis of varying systemic disease severity from 6 different farms. No predominant serotype was identified by farm or by systemic disease severity; however, the most fre-quent serotype, O158:NM (n = 3), was isolated from cows in the moderate severity group. Virulence genes evaluated were identified infrequently and were not associated with systemic disease severity. Evaluation of genetic similarity showed no clustering assigned by farm or mastitis severity based on systemic disease signs. We concluded that a high degree of genotypic variability is characteristic of E. coli strains causing clinical mastitis within and between different farms and systemic severity groups, and that specific cow fac-tors probably play amore important role in determining systemic disease severity. Key words: coliform mastitis, virulence, severit