Figure 3Biofilm formation with H2O2 treatment (range of 2.5 to 30mM) of strain N�� 1. (a) Biofilm biomass units (BBU) (–), relation of ROS and BBU (ROS/BBU) (-��-), and NO and BBU relation Tubacin molecular weight (NO/BBU, nitrite expressed in �� …3.2. Cytotoxic Effects on Vero CellsTo further evaluate the potential damage induced by Stx, the percentage of cytotoxicity was evaluated on Vero cells. The results summarized in Figure 4 indicate that the Stx release was observed from the biofilms in different growing conditions, being proportional to the stress observed of biofilms and it resulted into a significant increase in cellular toxicity. However, the maximum effect of cytotoxicity was observed with the supernatant treated with H2O2.Figure 4Vero cell cytotoxicity assay.

(a) The percent specific cytotoxicity was determined by microscopic quantification after staining the cells. (b) Micrographs of one representative independent experiment of strain N�� 1 are depicted (right). *P versus …4. Discussion Although outbreaks of STEC infections have been primarily associated with eating undercooked ground beef, a variety of other foods have also been implicated as vehicles. Moreover cross-contamination of foods can occur in food-processing plants and during subsequent handling and preparation, resulting in a wide range of foods being implicated in outbreaks of STEC infections. The ability of bacteria to attach to and produce biofilms on surfaces may influence their persistence during manufacturing and retail, as well as their ability to cause disease, with biofilm cells often being more resistant to various stresses than their planktonic counterparts [9, 10, 24].

Many investigations have disclosed that the presence of an appropriate sugar source is essential for the production of a polysaccharide matrix, with a low sugar concentration often being a limiting factor. Glucose, over a narrow concentration range, has been previously reported to increase biofilm formation [13, 25], and our results are in agreement with these results, since the clinical strain of E. coli O157:H7 (N�� 1) increased by 2.5-fold the biofilm formation, with other strains also leading to a higher formation, but to a lesser extent compared to strain N�� 1. We also found that mannose increased the biofilms. Biofilms formed under favorable conditions may protect STEC against the sanitizers used to decontaminate and produce processing environments [10].

Microcolony structures, due to endogenous oxidative stress, are specific sites within biofilms where Entinostat enhanced genetic adaptation and evolutionary change take place [26]. In addition, Boles and Singh showed that endogenous oxidative stress in biofilms promotes antibiotic resistance and that the addition of antioxidants reduces the diversity of biofilms [27].