Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2008
Publication Date: 6/1/2008
Citation: Karns, J.S., Van Kessel, J.S., Lombard, J.E. 2008. Prevalence of E. coli Virulence Factors in Raw Bulk Tank Milk from U.S. Dairy Farms. The American Society for Microbiology 108th General Meeting in Boston, Massachusetts, June 1- 5, 2008. Interpretive Summary:
Technical Abstract: Cattle are known reservoirs of zoonotic pathogenic bacteria and several outbreaks of disease have been associated with the consumption of raw milk or raw milk products. A national survey of US.. dairies was conducted during the National Animal Health Monitoring System’s (NAHMS) Dairy 2007 study to determine the prevalence of raw milk contaminated with pathogenic E. coli. Milk and inline milk filters were collected and shipped overnight to the laboratory. Milk was enriched in EC broth and milk filters were extracted in buffered peptone water prior to enrichment in EC broth. Multiplex real time PCR assays were used to determine the presence of the virulence genes stx1, stx2, eaeA and '-tir in the populations of organisms that grew in the enrichments. Shigatoxin genes (stx1 and/or stx2) were detected in 78 of 538 milk (14.5%) and 330 of 523 milk filter (63.1%) samples. The intimin gene (eaeA) was found to be present in 104 milk and 388 milk filter samples and was found in association with one or both stx genes in 30 milk and 266 milk filter samples. Seven milk samples (1.3%) were found to contain a combination of eaeA, '-tir, and stx1 and/or stx2 that might indicate the presence of the highly pathogenic strain O157:H7 while such a combination was found in extracts from 78 filters (14.9%). These data suggest that the incidence of detectable O157:H7 in bulk tank milk is low but there is the potential for contamination with other pathogenic forms. Since milk filters reflect what is entering the bulk tank these data suggest the potential for a high level of contamination with pathogenic E. coli. Milk filter analysis appears to be a more sensitive test of milk contamination by pathogenic bacteria than bulk tank milk analysis.