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Escherichia coli Isolates’ Serotypes, Genotypes, and Virulence Genes and Clinical Coliform Mastitis Severity

J. R. Wenz^*,1, G. M. Barrington, F. B. Garry^*, R. P. Ellis and R. J. Magnuson

^* Integrated Livestock Management, Department of Clinical Sciences, Colorado State University, Fort Collins 80526
Veterinary Teaching Hospital, Washington State University, Pullman 99164
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins 80526

¹ Corresponding author: jrwenz{at}colostate.edu

Dairy cattle with clinical mastitis caused by Escherichia coli exhibit a wide range of disease severity, from mild, with only local inflammatory changes of the mammary gland, to severe, with significant systemic derangement. 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 frequent 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 factors probably play a more important role in determining systemic disease severity.

Key Words: coliform mastitis • virulence • severity

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