Triclosan is a general membrane-active agent with a broad-spectrum antimicrobial activity that is commonly used in oral care products. In this study, we investigated the effect of sub-minimum inhibitory concentrations (MICs) of triclosan on the capacity of the cariogenic bacterium Streptococcus mutans to form biofilm and adhere to oral epithelial cells. As quantified by crystal violet staining, biofilm formation by two reference strains of S. mutans was dose-dependently promoted, in the range of 2.2- to 6.2-fold, by 1/2 and 1/4 MIC of triclosan. Observations by scanning electron microscopy revealed the presence of a dense biofilm attached to the polystyrene surface. Growth of S. mutans in the presence of triclosan at sub-MICs also increased its capacity to adhere to a monolayer of gingival epithelial cells. The expression of several genes involved in adherence and biofilm formation in S. mutans was investigated by quantitative RT-PCR. It was found that sub-MICs of triclosan significantly increased the expression of comD, gtfC, and luxS, and to a lesser extent of gtfB and atlA genes. These findings stress the importance of maintaining effective bactericidal concentrations of therapeutic triclosan since sub-MICs may promote colonization of the oral cavity by S. mutans.

In this study, we showed that supplementing the culture medium with fibrinogen induced biofilm formation by Streptococcus suis in a dose-dependent manner. Biofilm-grown S. suis cells were much more resistant to penicillin G than planktonic cells. S. suis bound fibrinogen to its surface, a property that likely contributes to biofilm formation.Streptococcus suis, a major swine pathogen worldwide, is transmitted via the respiratory route and colonizes the palatine tonsils of pigs (11). Although 35 serotypes (serotypes 1 to 34 and 1/2) have been identified, serotype 2 is considered the most prevalent and virulent in pigs (9). The major infections caused by this pathogen include septicemia, meningitis, and endocarditis (9). Zoonotic diseases caused by S. suis occur sporadically in individuals who work in close contact with pigs or pork by-products (7, 10).Biofilm formation by pathogenic microorganisms is a mechanism that allows them to become persistent colonizers, resist clearance by the innate and adaptive host immune system, enhance their resistance to antibiotics, and exchange genetic material (6). Biofilm formation is influenced by environmental parameters, such as the nature and availability of nutrients, which may modulate adhesin and polysaccharide production (15). We recently investigated the capacity of S. suis isolates to form biofilms and showed that this property was restricted to a few strains (8). In this paper, we report that fibrinogen induced biofilm formation by S. suis and increased its resistance to antibiotics.The basal broth medium used to investigate biofilm formation by S. suis S735, a virulent serotype 2 strain, contained 0.5% glucose, 2% peptone (proteose peptone no. 3; BBL Microbiology Systems), 0.3% K 2 HPO 4 , 0.2% KH 2 PO 4 , 0.01% MgSO 4 ⅐ 7H 2 O, 0.002% MnSO 4 ⅐ 6H 2 O, and 0.5% NaCl. An overnight culture of S. suis was diluted in fresh culture broth to obtain an optical density at 655 nm (OD 655 ) of 0.2. Samples (100 l) were added to the wells of a 96-well polystyrene tissue culture plate containing 100 l of culture medium. The effect on biofilm formation by S. suis of supplementing the medium with various mammalian proteins was investigated. The following proteins were added (5 mg/ml) to the basal broth medium: fibrinogen (human, bovine, and porcine), serum albumin (bovine), transferrin (human), gamma globulin (human), plasminogen (human), and mucin (porcine). Human fibrinogen was also tested at final concentrations of 0.5, 1, and 2 mg/ml. The plates were incubated for 18 h at 37°C, and bacterial growth was evaluated by determining the OD 655 using a microplate reader. Medium and free-floating bacteria were then removed, and biofilms were stained with crystal violet dye as previously described (8).As shown in Fig. 1, human, bovine, and porcine fibrinogens all induced marked biofilm formation. The effect was dose dependent and was observed at the lowest human fibrinogen concentration tested (0.5 mg/ml) (Fig. 2). Precoating the wells with fibrinogen (5 mg/ml for 2 h) did not induce b...

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Monocytes/macrophages are key members of the innate immune system and are present in higher numbers in active periodontal lesions than in inactive sites. The aim of this study was to characterize the response of human monocyte U937 cells, differentiated into adherent macrophages by treatment with phorbol-12-myristate 13-acetate, to stimulation by Fusobacterium nucleatum ssp. nucleatum lipopolysaccharide. Attachment of (3)H-lipopolysaccharide to macrophage-like cells was partially inhibited by anti-CD14 and anti-TLR4 polyclonal antibodies. Fusobacterial lipopolysaccharide did not cause cell apoptosis or block apoptosis induced by camptothecin. Lipopolysaccharide up-regulated the secretion of the pro-inflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha as well as the chemokine interleukin-8 by macrophage-like cells. In addition, it increased phospholipase C and D activities, which likely contributed to the high levels of prostaglandin E(2) detected in the cell culture supernatant. Lastly, the amount of matrix metalloproteinase-9 produced by macrophage-like cells was significantly increased by the lipopolysaccharide treatment. Interestingly, fusobacterial cells acquired matrix metalloproteinase-9 activity following incubation in the presence of the culture supernatant of lipopolysaccharide-stimulated macrophage-like cells. In summary, the lipopolysaccharide of F. nucleatum ssp. nucleatum has a large array of biological effects on macrophage-like cells. This monocytic responsiveness to lipopolysaccharide may be a key regulator of periodontitis.