Rapid Detection of Listeria spp. in Food and Environmental Samples by Esculin Hydrolysis

The use of Fraser Broth enables the presumptive detection of Listeria spp. within 48 h, thereby producing major cost and time savings when compared to existing methods. Fraser Broth was developed by modification of the USDA secondary enrichment broth through the addition of lithium chloride and ferric ammonium citrate. Esculin hydrolysis in Fraser Broth results in the production of a black precipitate. Since all Listeria spp. hydrolyse esculin, cultures which do not blacken can be considered to be Listeria -free. The efficacy of Fraser Broth was documented by testing a wide range of food and environmental samples from food processing facilities in parallel with the methods used by the government regulatory agencies. Fraser Broth inoculated from the USDA primary enrichment was found to be more sensitive than either Fraser Broth inoculated from the FDA enrichment or the existing FDA method in the analysis of ice cream products.