Biology of oral streptococci

Abstract

Warm, moist, and rich in nutrients, the oral cavity provides an ideal environment for colonization by a community of bacteria, fungi, protozoa, archaea, and viruses, often in the form of a complex structure called biofilm or plaque (1). In addition, several microbial niches exist within the oral cavity (e.g., cheek, gingiva, teeth, tongue, palate) that vary in nutrient content, pH, oxygen tension, and shear force due to salivary flow and mastication. These physico-chemical characteristics select for suitable microorganisms for each oral niche such that the microbial compositions can differ greatly from one site to another. Saliva is the biological fluid of the oral cavity, and its microbial composition is a collection of bacteria that have shed from various oral niches. As an easily accessible body fluid, saliva can be used in assessment of general oral health, as the disappearance or emergence of certain taxa can indicate health or disease (2, 3). While biofilms from oral soft tissues, such as the tongue, cheeks, and palate, and the supragingival biofilm (plaque on tooth surfaces above the gum line) are constantly bathed in saliva and subjected to an array of environmental fluctuations, the subgingival plaque (plaque on tooth surfaces below the gum line) is a unique niche with less abrupt environmental fluctuations. In particular, with the gum serving as a physical barrier, the oxygen tension and shear forces are reduced, and gingival crevicular fluid (serum) serves as a major nutrient source (4).