Salmonella strains (S. Heidelberg 271, S. Typhimurium 02:8423, S. Copenhagen PT 99, S. Enteritidis CRIFS 1016, and S. Kentucky 64701) were from the culture collection of the Food Science Department, University of Manitoba. Salmonella serovars were stored in BHI broth (Oxoid Ltd., Basingstoke, England) containing 25% (v/v) glycerol at 80 C. To activate the organisms, one loopful from each strainwas streaked on BHI agar (Oxoid) and incubated at 37 C for 24 he48 h. One colony of each Salmonella serovar was streaked on Xylose Lysine Deoxycholate (XLD) agar (Oxoid), and incubated at 37 C for 24 h. A single colony from the XLD agar was transferred to BHI broth and incubated overnight at 37 C. Salmonella
serovars were suspended again in BHI broth and incubated as before. Then, 0.1% (v/v) of this culture was transferred to fresh BHI broth and incubated overnight at 37 C. Either freshly prepared single cultures or mixtures of Salmonella cultures, prepared by combining equal volumes of each the 5 freshly cultured organisms in a sterile container, were used in the experiments.