RECOVERY and SPECIATION of LISTERIA FROM RAW and COOKED MEAT and POULTRY PRODUCTS

Abstract

Recovery of Listeria from raw and cooked meat products was compared using Fraser broth (FB) enrichment incubated at 30 and 35C for 24 and 48 h. the Micro-ID Listeria test strip for biochemical characterization of Listeria was also compared with conventional tests. Listeria spp. were recovered from 33, 47, and 20 of the raw chicken, raw beef and cooked meat products, respectively. No false-negative reactions were observed and more total Listeria-positive samples were found using FB incubated for 48 h compared with 24 h. Samples incubated at 35C had fewer false negative tubes than those incubated at 30C. More false-positive FB tubes were observed after 48 h than after 24 h incubation. Over half of the cooked samples did not hydrolyze the esculin and turn the tubes black, and therefore did not have to be streaked onto selective plates. However, with raw chicken or beef because of the large number of false-positive FB tubes, almost all tubes had to be streaked onto selective plates and very little advantage was gained from using the FB. the Micro-ID Listeria test kit gave a 100% correlation with conventional biochemical reactions for pure cultures of Listeria isolated from the three categories of meat products in this study. When used in conjunction with hemolysis plates and CAMP reactions, this test identifies species of Listeria isolates within 24 h of visible colony formation.