Evaluation of Fraser Broth to Isolate Listeria from Poultry

The detection of Listeria spp. from food samples without the need for subculture to agar plates means a big saving in time and money for routine monitoring of food products. The efficacy of the Adifferential system (esculin-ferric ammonium citrate) of Fraser broth as a screening test for the presence of Listeria spp. in raw chicken meat was investigated. The study was carried out on 100 eviscerated and refrigerated chicken carcasses; for isolation the USDA-FSIS method was used. One case (1% of positive samples) was false negative and three (60% of negative samples) false positives. Thus, the ability of the differential system to detect positive samples (sensitivity) was 98.95% and the ability to detect negative samples (specificity) was 40%. These data do not make this system very efficient as a screening test when working with food highly contaminated with other esculin positive microorganisms, as is the case with raw poultry meat.