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- Efficiency of four secondary enrichment protocols in differentiation and isolation of Listeria spp. and Listeria monocytogenes from smoked fish processing chainsPublication . Duarte, Gabriela; Vaz-Velho, Manuela; Capella, Christopher; Gibbs, PaulFour secondary enrichment protocols (conventional methods: UVM II, Fraser 24 h and Fraser 48 h: Impedimetric method: Listeria electrical detection medium) were studied for their ability to isolate Listeria spp. and Listeria monocytogenes from fish and environmental samples collected along the processing chain of cold-smoked fish. From all methods, Listeria spp. and L. monocytogenes were respectively present in 56 and 34 of 315 samples analysed. Fraser broth incubated for 48 h gave the fewest false negative Listeria spp. results [4/56; (7.1%)], but concurrently only 15/34 (44.1%) samples were correctly identified as containing L. monocytogenes. Listeria electrical detection (LED) medium detected only 36/56 (64.3%) Listeria spp. positive samples. Despite this lower isolation rate, LED identified 20/34 (58.8%) L. monocytogenes positive samples correctly and gave fewer false positive results. The overall conclusion was that more than one isolation method is needed to accurately estimate L. monocytogenes contamination rates.
- Evaluation of mini-VIDAS rapid test for detection of Listeria monocytogenes from production lines of fresh to cold-smoked fishPublication . Vaz-Velho, Manuela; Duarte, Gabriela; Gibbs, PaulThis study was conducted to evaluate the efficacy of the mini-VIDAS Listeria monocytogenes (LMO) system (BioMe´rieux Vitek, Inc., Missouri, USA) for detection of L. monocytogenes in environmental and fish samples from three Portuguese cold-smoking plants and from their fresh fish suppliers. Mini-VIDAS-LMO is a fully automated system that uses fluorescent ELFA (Enzyme Linked Fluorescent Assay) technology for detection of Listeria monocytogenes antigens in food. It can be a rapid screening method alternative to time consuming classical isolation and identification. Two hundred and ninety five samples were tested in mini-VIDAS-LMO and in parallel by the ISO 11290-1 traditional protocol. The mini-VIDAS-LMO detected 8 of the 11 confirmed positive samples and presented 11 false positive results. The specificity of the mini-VIDASLMO found in this experiment was 0.96 and the sensitivity 0.73