Abstract The pathogenic bacterium Listeria monocytogenes can persist in food processing plants for many years, even when appropriate hygienic measures are in place, with potential for contaminating ready-to-eat products and, its ability to form biofilms on abiotic surfaces certainly contributes for the environmental persistence. In this research, L. monocytogenes was grown in biofilms up 8 days attached to stainless steel and glass surfaces, contributing for advancing the knowledge on architecture of mature biofilms, since many literature studies carried out on this topic considered only early stages of cell adhesion. In this study, biofilm populations of two strains of L. monocytogenes (serotypes 1/2a and 4b) on stainless steel coupons and glass were examined using regular fluorescence microscopy, confocal laser scanning microscopy and classic culture method. The biofilms formed were not very dense and microscopic observations revealed uneven biofilm structures, with presence of exopolymeric matrix surrounding single cells, small aggregates and microcolonies, in a honeycomb-like arrangement. Moreover, planktonic population of L. monocytogenes (present in broth media covering the abiotic surface) remained stable throughout the incubation time, which indicates an efficient dispersal mechanism, since the culture medium was replaced daily. In conclusion, even if these strains of L. monocytogenes were not able to form thick multilayer biofilms, it was noticeable their high persistence on abiotic surfaces, reinforcing the need to focus on measures to avoid biofilm formation, instead of trying to eradicate mature biofilms.

OBJECTIVE: This study aimed to analyze and compare the microbiological profile and vitamin C content of raw and cooked foods destined for neutropenic inpatients. METHODS: Three vegetables and nine fruits, raw and boiled, washed and sanitized were examined. Heat-tolerant coliforms and coagulase-positive staphylococci were counted and the presence of Salmonella spp was investigated. The vitamin C content was analyzed by a colorimetric reaction. The Statistical Package for Social Sciences (SPSS) software was used for statistical analysis and the nonparametric Wilcoxon test was used to compare the mean vitamin C values of the cooked and raw foods. The Spearman correlation test was applied to determine the associations between the parameters evaluated RESULTS: Salmonella spp was absent in all samples and the populations of coagulase-positive staphylococci and heat-tolerant coliforms were below the minimum detectable limits of the methods employed (< 100 colony forming units (CFU)/g and < 3 most probable number (MPN)/g, respectively). There was a significant loss of vitamin C in the cooked foods, 38.9% on average, compared to the raw foods, a loss that was positively correlated with cooking time. CONCLUSION: The fresh fruits and vegetables properly sanitized in this study had a microbiological profile consistent with that required by Brazilian law. Furthermore, the nutritional value of the neutropenic diet is diminished, at least in terms of the vitamin C content.

Bactérias láticas são importantes em alimentos por apresentarem características probióticas e poderem ser empregadas como bioconservantes devido à capacidade de produzirem compostos antimicrobianos. No presente trabalho, a bacteriocina produzida por Enterococcus faecium 130, isolado de alimentos, foi parcialmente purificada e caracterizada. O composto apresentou ação inibitória na multiplicação de bactérias Gram-positivas, incluindo Listeria monocytogenes. Foi produzida em uma ampla faixa de temperatura (4 e 37 °C), estável em pH variando de 2 a 10 e não houve perda de atividade após aquecimento a 100 °C por 15 minutos. A purificação parcial da bacteriocina foi realizada pela técnica de adsorção-dessorção e o produto foi analisado por SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), sendo determinada a massa molecular aproximada entre 3,5 e 6,5 kDa. Os resultados obtidos estimulam novos estudos sobre a aplicação da bacteriocina em alimentos como uma barreira adicional contra a contaminação microbiana.

Lactic acid bacteria are important in foods as potential probiotics and also due to the ability to produce antimicrobial compounds that can contribute for biopreservation. In this work, the bacteriocin produced by the food isolate Enterococcus faecium 130 was partially purified and characterized. The compound was active against Gram-positive bacteria, including Listeria monocytogenes. It was produced after 4 days of storage at a broad temperature range (4 to 37 °C); it was stable at pH ranging from 2 to 10 with no loss of activity after heating at 100 °C for 15 minutes. Bacteriocin was partially purified by the adsorption-desorption technique, and the analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a molecular mass of 3.5 to 6.5 kDa. These data encourage studies on application of this bacteriocin in food systems as an additional hurdle to microbial growth.

Listeria monocytogenes é um patógeno transmitido por alimentos que apresenta a capacidade de sobreviver em biofilmes e persistir em plantas de processamento de alimentos. O presente trabalho avaliou a habilidade de Leuconostoc mesenteroides (bac+ e bac-) de inibir a formação de biofilme por L. monocytogenes ATCC 19115 em lâminas de aço inoxidável imersas em caldo BHI com ou sem sacarose em combinação com bactérias láticas (BAL). As células aderidas nas lâminas foram coletadas com swabs e enumeradas em meios seletivos (Oxford para listeria e MRS para leuconostoc). Leuconostoc mesenteroides bac+ foi efetivo na inibição da formação de biofilme por L. monocytogenes por até 3 horas de incubação. Entretanto, após 24 horas de incubação, foi verificada a formação de biofilme em todas as condições testadas, conforme evidenciado pelas imagens obtidas por meio de Microscopia Eletrônica de Varredura (MEV). Adicionalmente, foi observado um elevado número de células de L. monocytogenes alongadas na presença de L. mesenteroides bac+ em BHI adicionado de sacarose, indicando uma resposta de adaptação do patógeno às condições de estresse, com importantes implicações para a segurança alimentar.

Listeria monocytogenes is a foodborne pathogen which may survive in biofilms and persist in food processing plants. In this study, the ability of Leuconostoc mesenteroides (bac+ and bac-) to inhibit biofilm formation by L. monocytogenes ATCC 19115 was studied with stainless steel coupons immersed in BHI broth and BHI broth plus sucrose in combination with the Lactic Acid Bacteria (LAB). Adhered cells were collected with swabs and enumerated on selective agars (Oxford for listeria and MRS for leuconostoc). Leuconostoc mesenteroides bac+ in co-culture with L. monocytogenes was effective to inhibit biofilm formation by listeria for up to 3 hours of incubation, but at 24 hours, biofilm was present in all conditions tested, as confirmed by observations of stainless steel coupons under Scanning Electron Microscopy (SEM). It was also observed that in the presence of L. mesenteroides bac+ in BHI plus sucrose, a high number of elongated cells of L. monocytogenes was present, which may indicate an adaptation response of the pathogen to stress conditions with important implications for food safety.