Prevalence of foodborne pathogens in bulk tank milk

Bulk tank milk from 131 dairy herds in eastern South Dakota and western Minnesota was examined for the presence of for foodborne pathogens. Campylobacter jejuni, shiga-toxin producing Escherichia coli, Listeria monocytogenes, Salmonella spp., and Yersinia enterocolitica were detected in 9.2, 3.8, 4.6, 6.1, and 6.1% of bulk tank milk samples, respectively. Thirty-five of 131 (26.7%) bulk tank milk samples contained one or more species of pathogenic bacteria. Isolates of Salmonella belonged to group D (n = 4), B (n = 2), C (n = 1), and E (n = 1) "O" serogroups. All six isolates of Listeria monocytogenes were identified as O antigen type 1. Four of five isolates of E. coli encoded for the shiga-toxin 2 gene, while one strain encoded for the shiga-toxin 1 gene. Escherichia coli O157:H7 was not isolated from bulk tank milk samples. Based on autoagglutination testing, it was inferred that all eight isolates of Yersinia enterocolitica were likely to be virulent. Non A-grade (manufacturing grade) raw milk producers were at a higher risk (odd's ratio, 4.98; confidence interval, 1.96 to 12.22) of having one or more pathogens in their bulk tank milk than were Grade A producers. It was observed that 21 of 79 (26.6%) dairy producers who consumed raw milk had one or more pathogenic bacteria in their bulk tank milk. The findings of the study warrant the need for educational programs for dairy producers about the risks associated with consumption of raw milk.