Abstract
To persist in the oral cavity, bacteria must be able to tolerate rapid and substantial environmental fluctuations, particularly in pH and nutrient source and availability. Various species of Streptococcus, one of the most abundant genera in the mouth, are associated with oral health, as well as with dental caries. Cariogenic streptococci depend on a biofilm lifestyle for survival and persistence in the oral cavity and have developed sophisticated mechanisms to cope with environmental stresses. Here, we analyze the primary factors that allow these bacteria to emerge as significant members of tooth biofilms during adverse conditions. Our focus is on the molecular mechanisms of biofilm formation, stress tolerance and sugar metabolism by pathogenic oral streptococci, mainly Streptococcus mutans. Overlaps in the roles and regulation of these virulence attributes are highlighted and areas of research that deserve further investigation are proposed.
Highlights
The oral cavity is a dynamic environment that undergoes rapid and often substantial changes in pH, nutrient availability, carbohydrate source and oxygen tension
Among the most abundant microorganisms in the mouth, the oral streptococci are represented by species that are associated with oral health, as well as by species that are primarily associated with disease
Streptococci are widely distributed in the oral cavity, and include soft tissue colonizers, such as Streptococcus salivarius, S. oralis and S. mitis, as well as hard surface colonizers, such as S. mutans, S. sobrinus and S. gordonii
Summary
The oral cavity is a dynamic environment that undergoes rapid and often substantial changes in pH, nutrient availability, carbohydrate source and oxygen tension. Of the many environmental stresses to which oral biofilms are exposed, low pH and profound changes in carbohydrate source and availability appear to have the greatest impact on supragingival plaque ecology and the development of dental caries. Biofilm Formation Formation of oral biofilms on the hard tissues of the mouth is initiated by specific interactions between adhesins on the surface of oral bacteria and receptors of host and bacterial origin coating the surfaces of the teeth. Viridans streptococci, such as S. gordonii, S. mitis and S. sanguinis, and gram-positive rods such as Actinomyces spp., serve as pioneer bacteria that initiate the formation of dental plaque. Defects in stress-responsive genes have been associated with biofilm-impaired phenotypes (Baev et al, 1999; Lemos and Burne, 2002; Lemos et al, 2001; Lis and Kuramitsu, 2003)
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