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Chapter 1 : The Oral Microbial Ecosystem and Beyond
Category: Food Microbiology; Applied and Industrial Microbiology
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The oral cavity environment is anatomically, physiologically, and microbiologically diverse. Oral microbial communities exist primarily as multispecies biofilms on the surfaces present in the oral cavity, although large numbers of organisms are also present in the fluid phase of the saliva. The microbial biofilm communities that develop in the oral cavity are clearly intrinsically driven by bacterial interactions, but they are also host driven. Factors such as age, immune status, hormone levels, salivary flow rate, smoking, and dental hygiene standards impact on oral microbial community formation and composition. Dietary factors and antibiotic usage both have major influences. Better understanding of population shifts and what causes them will inform future strategies that may include attempting to recolonize disease sites with more healthy communities. Despite the fact that most oral disease conditions are associated with oral bacteria, the communities that develop in the mouth do largely retain harmonious relationships with the host over long periods. The chapter talks about effect of diet on oral microbial communities. The antibiotic resistance gene pool within the oral microflora and the ability of oral bacteria to readily exchange genetic information within the close confines of biofilms reflect the potential for widespread transfer of antibiotic resistance genes across commensal, pathogenic, and food-borne bacteria.
Diagrammatic representation of the incidence of major bacterial genera found in healthy dental plaque from the tooth surface and in subgingival plaque associated with periodontal disease. Subgingival plaque differs from tooth surface plaque in containing a greater variance of bacterial taxa and a higher proportion of gram-negative bacteria (gray shading). Data summarized and condensed from references 2 and 46 .
Schematic (not to scale) model of initial events leading to P. gingivalis-S. gordonii heterotypic biofilm community development on the supragingival tooth surface. S. gordonii (spheres) is a pioneer colonizer, and cells attach to the saliva-coated tooth surface. S. gordonii produces multiple adhesins, many of which have cognate salivary receptors; for simplicity, only SspA/B is shown. Initial localization of P. gingivalis (rods) is mediated by FimA interaction with GAPDH on the streptococcal surface. Higher-affinity binding occurs through engagement of Mfa with SspA/B. This interaction initiates a signal transduction event that modulates the P. gingivalis transcriptome. The resulting phenotypic adaptation of P. gingivalis, along with the production of signaling molecules such as AI-2, is necessary for the recruitment of additional P. gingivalis cells from the planktonic phase and the initiation of community development. Note that this is only one developmental stage of the process that leads to a mature heterotypic biofilm.
Adhesion and internalization of S. aureus by cultured osteoblasts. Staphylococci adhere avidly in groups to osteoblasts growing on titanium surfaces (A). Cellular projections entrap the staphylococci, and individual bacterial cells within these groups induce membrane ruffling and become internalized (B). Arrows indicate internalized bacteria. Bars, 1 μm. Images provided by C. M. Moffatt and T. Sjöström.
Factors influencing the transition from health-associated to disease-associated biofilms (top) and intervention strategies potentially able to induce a reverse transition (bottom). Increased incidence of antibiotic resistance within the oral microflora is promoted by genetic exchange within biofilms, with antibiotic usage driving the development and retention of less susceptible commensals and pathogens.