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- Characterization of Listeria monocytogenes isolated from production lines of fresh and cold-smoked fishPublication . Vaz-Velho, M.; Duarte, G.; McLauchlin, J.; Gibbs, P.Aims: The aims of this study were to characterize strains of Listeria monocytogenes isolated from cold-smoking fish plants to establish possible routes of contamination through the processing chain. Methods and Results: Listeria monocytogenes from fresh fish suppliers, raw materials, factory sites and finished products isolated in Portugal (162 isolates) and England (28 isolates) were characterized by serotyping, phage typing, tetracycline, cadmium and arsenic resistance, and plasmid profiling. On the basis of serotyping and phage typing, the isolates were categorized into eight groups. Although cultures within some of the groups could be further differentiated on the basis of plasmid profiling and cadmium and arsenite typing, consideration of all typing data predominantly clustered together isolates from a single location. L. monocytogenes strains: from fresh salmon suppliers were not found in the processing lines; from fresh salmon from different locations differed; and from the water where salmon trout were farmed differed from those isolated from the fish samples. Significance and Impact of the Study: No clear source or route of contamination in the cold-smoked processing chain could be established; however, these results highlight the complexity in tracking this bacterium through food chains.
- Evaluation of enhanced haemolysis agar for detection of Listeria spp. and L. monocytogenes from production lines of fresh to cold-smoked fishPublication . Vaz-Velho, Manuela; Duarte, Gabriela; Gibbs, PaulEnhanced haemolysis agar (EHA) was compared to the two conventional Listeria isolation agars Oxford and PALCAM for its ability to detect Listeria spp. from production lines of fresh to cold-smoked fish. The ability of EHA for distinguishing L. monocytogenes colonies from other Listeria spp. was also evaluated. A total of 243 fish and environmental samples were analysed. Overall, 42 samples were found to contain Listeria spp. Only 34 samples were positive simultaneously by the three plating media. Two samples considered to be negative by the two conventional agars were found to be positive after isolation on EHA. All three selective agars were shown to be less effective in recovering Listeria spp. after primary enrichment in half-Fraser broth, compared to secondary enrichment in Fraser broth after 24 and 48 h. From 79 Listeria but presumptive negative L. monocytogenes colonies, EHA identified correctly 76 Listeria spp. and presented three false-negative results_three colonies further identified as L. monocytogenes but showing no noticeable haemolysis on EHA. Twenty-three of the thirty-three L. monocytogenes presumptive positive colonies, were confirmed positive and ten were identified as L. seeligeri. Despite its ability of distinguishing L. monocytogenes from the other Listeria spp., unless it is produced as a commercial medium, EHA cannot be an alternative to time-consuming classical identification because the preparation of this medium is both time and labour intensive.
- Comparison of two pre-enrichments broths for recovering Listeria spp. from salmon (Salmo salar) and salmon-trout (Oncorhynchus mykiss)Publication . Vaz-Velho, Manuela; Duarte, Gabriela; Gibbs, PaulLow levels of occurrence of Listeria spp. in fresh salmon (Salmo_salar ) and salmon-trout (Oncorhynchus mykiss), may be related to the selectivity of the pre-enrichment broth recommended by ISO 11290-1. The purpose of this study was to compare the abilities of Fraser base (without supplements) and 0.1% (w/v) peptone water for recovering Listeria spp. from the fresh fish samples. Fifty-six fish were swabbed and the swabs placed in Fraser base and in 0.1% (w/v) peptone water. Samples were analysed 4–6 h later following the ISO 11290-1 protocol. A total of fifteen Listeria spp. positive samples were found. Three and twelve samples were found to contain respectively, L. monocytogenes and L. innocua. The Fraser base did not detect any of the three L. monocytogenes positive samples. Only two Listeria spp. positive samples were simultaneously recovered by the two broths.
- 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
- Comparison of milk from two different cow breeds Barrosã and FrísiaPublication . Pires, Preciosa; Fernandes, Élia; Vilarinho, Manuela; Barros, Mário; Ferreira, Rita; Carneiro, Luísa; Almeida, Gonçalo; Vaz-Velho, ManuelaMilk from two different cow breeds, Barrosã and Frísia, was studied. Within the same breed five and four milk samples were taken respectively for chemical and microbiological analysis. The following chemical parameters were analysed in triplicate: Total Fat, Fatty Acids Identification and Quantification, Protein, Casein, Albumin, Non-protein Nitrogen, Vitamin A, Vitamin D, Phosphorus, Potassium, Sodium, Iron, Magnesium, Calcium, Ash, Total solids, Lactic acid and Acidity. In general terms milk from Barrosã breed showed higher values for all analysed parameters except for Total Fat, Total Solids and Vitamin D. Statistical analysis, by testing the chemical parameters all together using the Hotelling T2 test showed that milk samples from the two cow breeds were significantly different (α=0,05). Microbiological analysis (Total Viable Counts (30ºC), Escherichia coli, Staphylococcus coagulase + and Listeria monocytogenes) was also performed. Staphylococcus coagulase + was found in one milk sample from Barrosã breed. Listeria monocytogenes was found in two milk samples from Frísia breed.
- Is Listeria innocua 2030c, a tetracycline-resistant strain, a suitable marker for replacing L. monocytogenes in challenge studies with cold-smoked fish?Publication . Vaz-Velho, Manuela; Fonseca, Fátima; Silva, Manuela; Gibbs, PaulThe suitability of Listeria innocua 2030c, a tetracycline-resistant strain, to be used as an indicator for replacing Listeria monocytogenes in challenge studies with cold-smoked fish was ascertained. L. innocua 2030c was compared to serovars 4b and 1/2c of L. monocytogenes, the major types isolated from Portuguese cold-smoked fish products. Growth curves at 30°C, growth/survival patterns at 30°C under exposure to different times and concentrations of ozone and sensitivity to Carnobacterium divergens V41 and C. piscicola V1 and their bacteriocins V41 and V1, were determined. No important differences between L. innocua 2030c and L. monocytogenes 4b and 1/2c were found, therefore L. innocua 2030c can be considered a suitable indicator for replacing those L. monocytogenes strains in challenge studies. Author Keywords: Carnobacterium spp.; Listeria spp.; Ozone