Growth, viability and architecture of biofilms of Listeria monocytogenes formed on abiotic surfaces

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.

Microbiological profile and nutritional quality of raw foods for neutropenic patients under hospital care

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.