A total of 66 samples of seafood were tested for the presence of Listeria monocytogenes and other Listeria species. Listeria spp. were present in 23% of the samples (15/66) of them, 10 isolates were characterized as L. innocua (66.67%), 2 L. monocytogenes (13.33%), 1 L. grayi (6.67%), 1 L. seeligeri (6.67%) and 1 L. ivanovii (6.67%). Of the total bacterial isolates, the 20% (3/15) showed ability to form biofilm, identified as 2 species of L. innocua and 1 L. monocytogenes. The anti-Listeria activity of aqueous extracts of A. caven, A. furcatispina, P. torquata and N. cataria and their combinations was determined. The aqueous extract of P. torquata and N. cataria showed the highest inhibitory activity against strains of Listeria (2.5 mg/mL and 5 mg/mL respectively). The antibacterial activity was enhanced by the mixture of some extracts. The combinations of A. caven + A. furcatispina and A. furcatispina + P. torquata showed beneficial effect to inhibit the growth of Listeria. The fractional inhibitory concentration (FIC) index for this mixture indicated an additive effect (FIC = 0.75 and 0.56 respectively), while the remaining combinations showed indifferent effect. However, none of natural products, as well as all mixtures showed inhibitory activity in biofilm formation by Listeria at least, under the conditions assayed.Fil: Mohamed, Ana Mariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Cifuente, Diego Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Mattana, Claudia Maricel. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia; Argentin
