EVALUATION OF UNIVERSAL PREENRICHMENT BROTH FOR THE RECOVERY OF FOODBORNE PATHOGENS FROM MILK AND CHEESE

The use of universal preenrichment broth for the recovery of verotoxig enic Escherichia coli, Salmonella spp., and Listeria monocytogenes fro m milk and cheese was examined. Universal preenrichment broth supporte d the growth of low inoculum levels (10 cfu/ mi) 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 supporte d the recovery and growth of heat-injured Salmonella spp., L. monocyto genes, and verotoxigenic E. coli at inoculum levels of 10(2) cfu/ml to yield cell levels of 10(8) cfu/ml in pure cultures and at least 10(5) cfu/ml in the presence of high levels of known competitive pathogens or microflora of cheese samples after 24 h of incubation. Universal pr eenrichment broth performed better than Listeria enrichment broth in s upporting 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 universa l preenrichment broth reduced the quantity of milk or cheese samples t hat were required for analysis and also reduced the cost and labor inv olved in preparing and processing separate preenrichment media.