Inhibitory effect of bacteriocins from enterococci on developing and preformed biofilms of Listeria monocytogenes, Listeria ivanovii and Listeria innocua.

The biofilm-forming ability of Listeria spp. is a concern to the food industry and health sectors. The aim of this study was to verify the inhibitory activity of bacteriocins produced by enterococci (Enterococcus faecium 20, 22 and 24 and Enterococcus faecalis 27) on developing biofilm and preformed biofilm of Listeria species. Bacteriocins were partially purified from cell free supernatant (CFS). L. monocytogenes 2032, L. innocua 2050 and L. ivanovii 2056 were selected to analyse the inhibitory effect of bacteriocins on biofilm biomass (crystal violet staining) and biofilm viability (XTT-reduction). The biomass of the developing and preformed biofilms of Listeria species were reduced (p < 0.05) in the presence of all bacteriocins tested. Overall, the reduction in biofilm biomass of developing biofilms was up to 87.4% for bacteriocin produced by E. faecium 22 (CFS22) against L. ivanovii and up to 87.1% for CFS22 against L. monocytogenes. These findings are in accordance with those observed in confocal microscopy analysis. Most of the CFS-containing bacteriocin (CFS22, CFS24, CFS27) were effective at decreasing the viability of biofilm cells from all Listeria species. The highest reduction in viability was observed for L. monocytogenes preformed biofilm cells (up to 98.7%), evidenced by fluorescence microscopy of propidium iodide-labelled cells. Scanning electron microscopy showed that cells of biofilm-treated bacteriocins displayed degenerative changes that may be indicative of cellular leakages. This study suggests that bacteriocins produced by enterococci have prospective applications to prevent biofilm formation and/or to reduce cell viability of formed biofilms of distinct Listeria species.

Antimicrobial activity of enterocin obtained from Enterococcus durans on Shiga-like toxin-producing Escherichia coli / Atividade antimicrobiana de enterocina produzida por Enterococcus durans sobre Escherichia coli produtora de toxina Shiga-like

ABSTRACT: Shiga-like toxin-producing Escherichia coli (STEC) is an important source of food contamination that presents risks to human health. Several industrial food processes eliminate this microorganism; however, these processes can alter the characteristics of the product. Alternative methods of preservation have been identified as an option to control these foodborne pathogens. The purpose of this study was to evaluate the action of bacteriocins produced by Enterococcus durans MF5 in STEC cells. Cell-free supernatant (CFS) containing enterocins from the MF5 isolate was tested over different time points (6, 18, and 24 h). Enterocins present in the crude CFS showed inhibition against STEC at all time points. In the investigation of cell integrity, using propidium iodide and fluorescence microscopy, considerable cell death was observed within 6 h of the cells being in contact with the enterocins, which was also observed at the 18 and 24 h time points. These results showed that the enterocins produced by the MF5 isolate have potential use in the control of STEC.

RESUMO: Escherichia coli, produtora de toxina Shiga-like (STEC), apresenta riscos à saúde humana, constituindo uma importante fonte de contaminação na indústria de alimentos. Diversos processos industriais eliminam esse microrganismo, contudo podem alterar as características do produto. Métodos alternativos de conservação tem sido uma opção para controlar esse microrganismo de alimentos. O objetivo desta pesquisa foi avaliar a ação de bacteriocinas produzidas por Enterococcus durans MF5 em células de E. coli STEC. Foram utilizados sobrenadante livre de células (CFS) contendo enterocina, nos tempos 6, 18 e 24 horas de incubação. A enterocina presente no CFS bruto apresentou inibição contra E. coli STEC em todos os tempos testados. Na observação da integridade celular utilizando iodeto de propídio e observação em microscópio de fluorescência, observou-se que em 6h da célula em contato com a enterocina, já havia considerável morte celular, estendendo até os tempos de 18 e 24 horas. Os resultados obtidos mostraram que a enterocina produzida pelo isolado MF5 apresenta uso potencial no controle de E. coli STEC.