Evaluation of the Serobact ™ and Microbact ™ systems for the detection and identification of Listeria spp.

Abstract

The Serobact ™ Listeria latex agglutination reagent and Microbact ™ 12L system were evaluated, respectively, for the detection and identification of Listeria in foods. The Serobact ™ reagent proved effective, compared with conventional cultural methods, in the detection of low levels (1–10 cells/25 g) of both L. monocytogenes and L. innocua artificially inoculated into a range of foods, following enrichment. Extended incubation of either the primary or secondary enrichment increased the number of samples positive for Listeria by both Serobact ™ and conventional culture, but also increased the number of false positive reactions. The Serobact ™ reagent also proved effective in screening enrichment cultures of potentially contaminated retail food samples. Using the USDA enrichment procedure, the Serobact ™ reagent yielded 100% sensitivity and 93.9% specificity, when compared to conventional culture. Identification of 81 Listeria isolates using the Microbact ™ 12L system was compared with conventional biochemical and physiological tests. While identification after 4 h was poor, due to negative or incomplete fermentation of carbohydrates and lack of haemolysis, identification of all but two of 81 isolates was achieved after 24 h.