Effects of high levels of selenite and Escherichia coli on enrichment of Salmonella and detection of Salmonella by polymyxin-cloth enzyme immunoassay

The effect of various concentrations of selenite on the recovery of Salmonella typhimurium and Escherichia coli was examined in a rich medium containing 0.5% cholate. For heat-injured S. typhimurium, longer preincubation periods were required for recovery in higher concentrations of selenite. When 0.7% selenite was added to 6-h preincubated cultures of heat-injured cells, S. typhimurium was fully recovered while E. coli, whether heat-injured or uninjured, did not recover when present at numbers at less than 2 × 107 colony forming units (CFU). The polymyxin-cloth enzyme immunoassay detected S. typhimurium grown from a small number (as low as 1 CFU) of cells in the presence of a large excess of E. coli.