Microbial ecosystem in the oral cavity: Metabolic diversity in an ecological niche and its relationship with oral diseases

doi:10.1016/j.ics.2005.06.071

International Congress Series

Volume 1284, September 2005, Pages 103-112

https://doi.org/10.1016/j.ics.2005.06.071 Get rights and content

Abstract

With the respect to microbial flora, the oral cavity is one of the most densely populated sites of the human body. The environmental diversity of the oral cavity promotes the establishment of distinct microbial communities, such as supragingival plaque, subgingival plaque and tongue coating. The properties of the environment determine which microorganisms can occupy a site, while the metabolic activities of those microbial communities subsequently modify the properties of the environment. Saccharolytic microorganisms in supragingival sites ferment carbohydrates into, principally, lactic acid and create a temporarily acidic environment. Conversely, in subgingival sites, asaccharolytic microorganisms metabolize nitrogenous compounds derived from gingival crevicular fluid (GCF) and create a neutral pH and anaerobic environment abundant in short-chain fatty acids and ammonia. In tongue coating, asaccharolytic activity toward cysteine and methionine produces sulfur compounds, the major components of oral malodor. Furthermore, changes in environmental factors can prompt the development of adaptive responses in individual microorganisms to new environmental conditions and introduce more pathogenic microorganisms into the microbial community. Non-mutans streptococci and Actinomyces are predominant in the supragingival ecosystem that cause acidification, resulting in both demineralization of tooth surface and introduction of more cariogenic microorganisms, mutans streptococci, to the ecosystem. Fusobacteria and Prevotella neutralize subgingival environment pH by nitrogenous metabolism and stimulate GCF efflux. The neutral pH and nitrogenous environment increases the proteolytic activity of Prevotella and facilitates the establishment of a more acid-intolerant, but periodontopathogenic bacterium, Porphyromonas gingivalis. An environment determined by microbial metabolic activity can characterize a microbial ecosystem, and environmental changes originated by metabolic activity can often modify microbial physiological activity, initiating a shift from healthy to pathogenic conditions in this microbial ecosystem.

Section snippets

Bacterial pathogenicity in a microbial ecosystem—ecological plaque hypothesis

Oral cavity is the entrance of the digestive tract, which is often regarded as the ‘inner outside’. The digestive tract is anatomically continuous and harbors approximately 1 × 10¹⁴ microorganisms, which is more than the approximately 6 × 10¹³ cells that constitute the entire human body. Of the various site of the body, the oral cavity is one of the most densely populated and in excess of 500 microorganism species have been isolated from the oral cavity using recently developed molecular biological

Diverse ecological niches in the oral cavity

The heterogeneity of tissue types in the oral cavity, such as teeth, tongue and mucosa, means that a variety of sites are available for colonization by oral microorganisms. Each site has unique characteristics and allows those microorganisms best suited to the environment to inhabit the site. The function or role of microorganisms in a habitat is referred as an ecological niche and a number of ecological niches exist in the oral cavity, including supragingival plaque, subgingival plaque and

Acid production from carbohydrate metabolism and adaptation to acid stress in the supragingival area

The supragingival area consists of the stable environment of the tooth surface coated with salivary components such as proteins and glycoproteins. This continuous supply of saliva acts as a nutrient supply for the microorganisms while carbohydrates derived from foods are also intermittently supplied (Table 2).

Streptococcus and Actinomyces species are predominant in the supragingival area. They can adhere the saliva-coated tooth surface by attachment between adhesins (located on bacterial cell

Protein, peptide and amino acid metabolisms in the subgingival area

Subgingival sites provide a stable tooth surface and an unstable epithelial surface, the latter of which continuously desquamates. Both surfaces are bathed with a continuous efflux of gingival crevicular fluid (GCF), derived from blood plasma and thus nutritionally rich in nitrogenous compounds such as amino acids, peptides and proteins. Desquamated epithelium can also be supplied as a nutrient (Table 3). As a gingival crevice deepens, the environmental factors in the subgingival site become

Tongue coating and oral malodor

Tongue coating consists of desquamated epithelium from the tongue, saliva and microorganisms, and as supragingival sites, food supply is intermittent (Table 3). The papillary structure of the dorsum of the tongue provides a suitable habitat for many microorganisms, and the environment can also be characterized by anaerobic conditions that are conducive for the growth of obligatory anaerobes. A wide range of bacteria including Actinomyces, Streptococci, Veillonella, Fusobacterium and Prevotella

Significance of metabolic activity in the microbial ecosystem

Recent developments of molecular biological techniques for microbial identification have clarified that oral microflora form a microbial complex, or biofilm, consisting of in excess of 500 microbial species. In addition, studies of interactions between bacterial cells and between bacteria and host cells are in the process of revealing that this microbial complex forms a community–a ‘microbial ecosystem’–in which microorganisms interact competitively and cooperatively. We are relatively familiar

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Microbial ecosystem in the oral cavity: Metabolic diversity in an ecological niche and its relationship with oral diseases

Abstract

Section snippets

Bacterial pathogenicity in a microbial ecosystem—ecological plaque hypothesis

Diverse ecological niches in the oral cavity

Acid production from carbohydrate metabolism and adaptation to acid stress in the supragingival area

Protein, peptide and amino acid metabolisms in the subgingival area

Tongue coating and oral malodor

Significance of metabolic activity in the microbial ecosystem

Arch. Oral Biol.

In vitro acidogenic potential and mutans streptococci of human smooth surface plaque associated with initial caries lesions and sound enamel

J. Dent. Res.

The association of mutans streptococci and non-mutans streptococci capable of acidogenesis at a low pH with dental caries on enamel and root surfaces

J. Dent. Res.

The final pH of bacteria comprising the predominant flora on sound and carious human root and enamel surfaces

J. Dent. Res.

Bacteriology of human gingivitis

J. Dent. Res.

Microbiota of health, gingivitis, and initial periodontitis

J. Clin. Periodontol.

Microbial ecology of dental plaque and its significance in health and disease

Adv. Dent. Res.

Adhere today, here tomorrow: oral bacterial adherence

J. Bacteriol.

Acid-induced acidogenicity and acid tolerance of non-mutans streptococci

Oral Microbiol. Immunol.

Hydrogen peroxide excretion by oral streptococci and effect of lactoperoxidase–thiocyanate–hydrogen peroxide

Infect. Immun.

Metabolic pathways for cytotoxic end-product formation from glutamate- and aspartate-containing peptides by Porphyromonas gingivalis

J. Bacteriol.

Pathways for amino acid metabolism by Prevotella intermedia and Prevotella nigrescens

Oral Microbiol. Immunol.

Pathways of glutamate catabolism among Fusobacterium species

J. Gen. Microbiol.