Shigatoxin producing Escherichia coli in dairy cattle in Northern Germany: prevalence and influences on shedding patterns

The relevance of Shigatoxin producing Escherichia coli (STEC) is justified by the caused serious diseases in combination with a low infectious dose. This study aimed for the identification and evaluation of risk factors in fecal shedding of STEC in dairy cows. The longitudinal design of the study permitted to follow the STEC-shedding of selected cows over the period of twelve months. Overall, 24.7% (407) of 1,646 fecal samples were positive for STEC by PCR. The inner herd prevalence varied from 11.1% to 32.3%. The month of sampling, the number of lactations and days in milk, the nutritional condition, the somatic cell count, the content of protein in milk and the presence of a continuously positive cow in the herd were identified to have a significant influence on shedding of STEC. As already confirmed for the serogroup O157, first calvers, cows in early lactation and dry cows also formed a group of higher risk for the other STECserogroups. The late summer months (August, September, and October) were analyzed as season with higher prevalences. Isolated bovine STEC mainly possessed the genes for stx2 and EHEC-hlyA (434 isolates, 39.3%), and stx1, stx2 and EHEC-hlyA (311 isolates, 28.1%), which represent potentially pathogenic virulence profiles for humans.