Abstract
BackgroundPrevotella intermedia (P. intermedia), a gram-negative, black-pigmented anaerobic rod, has been implicated in the development of chronic oral infection. P. intermedia strain 17 was isolated from a chronic periodontitis lesion in our laboratory and described as a viscous material producing strain. The stock cultures of this strain still maintain the ability to produce large amounts of viscous materials in the spent culture media and form biofilm-like structures. Chemical analyses of this viscous material showed that they were mainly composed of neutral sugars with mannose constituting 83% of the polysaccharides. To examine the biological effect of the extracellular viscous materials, we identified and obtained a naturally-occurring variant strain that lacked the ability to produce viscous materials in vitro from our stock culture collections of strain 17, designated as 17-2. We compared these two strains (strains 17 versus 17-2) in terms of their capacities to form biofilms and to induce abscess formation in mice as an indication of their pathogenicity. Further, gene expression profiles between these two strains in planktonic condition and gene expression patterns of strain 17 in solid and liquid cultures were also compared using microarray assays.ResultsStrain 17 induced greater abscess formation in mice as compared to that of the variant. Strain 17, but not 17-2 showed an ability to interfere with the phagocytic activity of human neutrophils. Expression of several genes which including those for heat shock proteins (DnaJ, DnaK, ClpB, GroEL and GroES) were up-regulated two to four-fold with statistical significance in biofilm-forming strain 17 as compared to the variant strain 17-2. Strain 17 in solid culture condition exhibited more than eight-fold up-regulated expression levels of several genes which including those for levanase, extracytoplasmic function-subfamily sigma factor (σE; putative) and polysialic acid transport protein (KpsD), as compared to those of strain 17 in liquid culture media.ConclusionThese results demonstrate that the capacity to form biofilm in P. intermedia contribute to their resistance against host innate defence responses.
Highlights
Prevotella intermedia (P. intermedia), a gram-negative, black-pigmented anaerobic rod, has been implicated in the development of chronic oral infection
Viscosity of spent culture medium Stock cultures of P. intermedia strain 17 were transferred to enriched-trypticase soy broth and grown for 48 h
Exopolysaccharide (EPS) is one of the main constituents of the biofilm extracellular matrix [21], and recent investigations have revealed that each biofilm-forming bacterium produces distinctive EPS components e.g. alginate and/or Psl found in Pseudomonas aeruginosa [22], acidic polysaccharide of Burkholderia cepacia [23], collanic acid, poly- -1,6-GlcNAc (PGA) or cellulose found in Escherichia coli [24,25,26,27], cellulose of Salmonella [24,28], amorphous EPS containing Nacetylglucosamine (GlcNAc), D-mannose, 6-deoxy-Dgalactose and D-galactose of Vibrio cholerae [29], polysaccharide intercellular adhesin (PIA) of Staphylococcus [30], and glucose and mannose rich components found in Bacillus subtilis biofilm [31]
Summary
Prevotella intermedia (P. intermedia), a gram-negative, black-pigmented anaerobic rod, has been implicated in the development of chronic oral infection. To examine the biological effect of the extracellular viscous materials, we identified and obtained a naturally-occurring variant strain that lacked the ability to produce viscous materials in vitro from our stock culture collections of strain 17, designated as 17-2 We compared these two strains (strains 17 versus 17-2) in terms of their capacities to form biofilms and to induce abscess formation in mice as an indication of their pathogenicity. P. intermedia strain 17 was initially isolated from a chronic periodontitis lesion in our laboratory [12] and some of its phenotypic characteristics were determined Among these included the ability of the organism to: (a) produce viscous materials in vitro [12]; (b) invade human oral epithelial cells [13]; and (c) stimulate CD4+ T cells expressing V 8, V 12 and V 17 [14]. We sought to determine the gene expression profiles associated with the biofilm formation by these two strains using microarray assays
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