Sucrose Substitutes Affect the Cariogenic Potential of Streptococcus mutans Biofilms

Streptococcus mutans is considered the primary etiologic agent of dental caries and contributes significantly to the virulence of dental plaque, especially in the presence of sucrose. To avoid the role of sucrose on the virulence factors of S. mutans, sugar substitutes are commonly consumed because they lead to lower or no production of acids and interfere with biofilm formation. This study aimed to investigate the contribution of sugar substitutes in the cariogenic potential of S. mutans biofilms. Thus, in the presence of sucrose, glucose, sucralose and sorbitol, the biofilm mass was quantified up to 96 h, the pH of the spent culture media was measured, the expression of biofilm-related genes was determined, and demineralization challenge experiments were conduct in enamel fragments. The presence of sugars or sugar substitutes profoundly affected the expression of spaP, gtfB, gtfC, gbpB, ftf, vicR and vicX in either biofilm or planktonic cells. The substitution of sucrose induced a down-regulation of most genes involved in sucrose-dependent colonization in biofilm cells. When the ratio between the expression of biofilm and planktonic cells was considered, most of those genes were down-regulated in biofilm cells in the presence of sugars and up-regulated in the presence of sugar substitutes. However, sucralose but not sorbitol fulfilled the purpose of reducing the cariogenic potential of the diet since it induced the biofilm formation with the lowest biomass, did not change the pH of the medium and led to the lowest lesion depth in the cariogenic challenge

Application of an active attachment model as a high-throughput demineralization biofilm model

Objectives: To investigate the potential of an active attachment biofilm model as a highthroughput demineralization biofilm model for the evaluation of caries-preventive agents. Methods: Streptococcus mutans UA159 biofilms were grown on bovine dentine discs in a highthroughput active attachment model. Biofilms were first formed in a medium with high buffer capacity for 24 h and then subjected to various photodynamic therapies (PACT) using the combination of Light Emitting Diodes (LEDs, Biotable (R)) and Photogem (R). Viability of the biofilms was evaluated by plate counts. To investigate treatment effects on dentine lesion formation, the treated biofilms were grown in a medium with low buffer capacity for an additional 24 h. Integrated mineral loss (IML) and lesion depth (LD) were assessed by transversal microradiography. Calcium release in the biofilm medium was measured by atomic absorption spectroscopy. Results: Compared to the water treated control group, significant reduction in viability of S. mutans biofilms was observed when the combination of LEDs and Photogem (R) was applied. LEDs or Photogem (R) only did not result in biofilm viability changes. Similar outcomes were also found for dentine lesion formation. Significant lower IML and LD values were only found in the group subjected to the combined treatment of LEDs and Photogem (R). There was a good correlation between the calcium release data and the IML or LD values. Conclusions: The high-throughput active attachment biofilm model is applicable for evaluating novel caries-preventive agents on both biofilm and demineralization inhibition. PACT had a killing effect on 24 h S. mutans biofilms and could inhibit the demineralization process. (C) 2011 Elsevier Ltd. All rights reserved.

Analysis of the biofilm proteome of Xylella fastidiosa

Abstract Background Xylella fastidiosa is limited to the xylem of the plant host and the foregut of insect vectors (sharpshooters). The mechanism of pathogenicity of this bacterium differs from other plant pathogens, since it does not present typical genes that confer specific interactions between plant and pathogens (avr and/or hrp). The bacterium is injected directly into the xylem vessels where it adheres and colonizes. The whole process leads to the formation of biofilms, which are considered the main mechanism of pathogenicity. Cells in biofilms are metabolically and phenotypically different from their planktonic condition. The mature biofilm stage (phase of higher cell density) presents high virulence and resistance to toxic substances such as antibiotics and detergents. Here we performed proteomic analysis of proteins expressed exclusively in the mature biofilm of X. fastidiosa strain 9a5c, in comparison to planktonic growth condition. Results We found a total of 456 proteins expressed in the biofilm condition, which correspond to approximately 10% of total protein in the genome. The biofilm showed 37% (or 144 proteins) different protein than we found in the planktonic growth condition. The large difference in protein pattern in the biofilm condition may be responsible for the physiological changes of the cells in the biofilm of X. fastidiosa. Mass spectrometry was used to identify these proteins, while real-time quantitative polymerase chain reaction monitored expression of genes encoding them. Most of proteins expressed in the mature biofilm growth were associated with metabolism, adhesion, pathogenicity and stress conditions. Even though the biofilm cells in this work were not submitted to any stress condition, some stress related proteins were expressed only in the biofilm condition, suggesting that the biofilm cells would constitutively express proteins in different adverse environments. Conclusions We observed overexpression of proteins related to quorum sensing, proving the existence of communication between cells, and thus the development of structuring the biofilm (mature biofilm) leading to obstruction of vessels and development of disease. This paper reports a first proteomic analysis of mature biofilm of X. fastidiosa, opening new perspectives for understanding the biochemistry of mature biofilm growth in a plant pathogen.