Evaluation of Universal Preenrichment Broth for the Recovery of Foodborne Pathogens from Milk and Cheese

¹ Laboratory Services Division, University of Guelph, Guelph, ON, Canada N1H 8J7
² Health of Animals Laboratory, Health Canada, Guelph, ON, Canada N1G 3W4

The use of universal preenrichment broth for the recovery of verotoxigenic Escherichia coli, Salmonella spp., and Listeria monocytogenes from milk and cheese was examined. Universal preenrichment broth supported the growth of low inoculum levels (10 cfu/ ml) of these organisms in pure cultures and in mixed cultures containing higher levels of other pathogens or bacterial flora from raw milk. This medium also supported the recovery and growth of heat-injured Salmonella spp., L. monocytogenes, and verotoxigenic E. coli at inoculum levels of 10² cfu/ml to yield cell levels of 10⁸ cfu/ml in pure cultures and at least 10⁵ cfu/ml in the presence of high levels of known competitive pathogens or microflora of cheese samples after 24 h of incubation. Universal preenrichment broth performed better than Listeria enrichment broth in supporting the recovery and growth of heat-injured L. monocytogenes and equally as well as buffered peptone water or trypticase soy broth in supporting the growth of uninjured L. monocytogenes, Salmonella spp., and verotoxigenic E. coli. Coenrichment of these pathogens in universal preenrichment broth reduced the quantity of milk or cheese samples that were required for analysis and also reduced the cost and labor involved in preparing and processing separate preenrichment media.

Key Words: universal preenrichment broth • food-borne pathogens • milk • cheese

Submitted on January 16, 1998
Accepted on July 6, 1998

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