Defining the Normal Bacterial Flora of the Oral Cavity

Abstract

More than 700 bacterial species or phylotypes, of which over 50% have not been cultivated, have been detected in the oral cavity. Our purposes were (i) to utilize culture-independent molecular techniques to extend our knowledge on the breadth of bacterial diversity in the healthy human oral cavity, including not-yetcultivated bacteria species, and (ii) to determine the site and subject specificity of bacterial colonization. Nine sites from five clinically healthy subjects were analyzed. Sites included tongue dorsum, lateral sides of tongue, buccal epithelium, hard palate, soft palate, supragingival plaque of tooth surfaces, subgingival plaque, maxillary anterior vestibule, and tonsils. 16S rRNA genes from sample DNA were amplified, cloned, and transformed into Escherichia coli. Sequences of 16S rRNA genes were used to determine species identity or closest relatives. In 2,589 clones, 141 predominant species were detected, of which over 60% have not been cultivated. Thirteen new phylotypes were identified. Species common to all sites belonged to the genera Gemella, Granulicatella, Streptococcus, and Veillonella. While some species were subject specific and detected in most sites, other species were site specific. Most sites possessed 20 to 30 different predominant species, and the number of predominant species from all nine sites per individual ranged from 34 to 72. Species typically associated with periodontitis and caries were not detected. There is a distinctive predominant bacterial flora of the healthy oral cavity that is highly diverse and site and subject specific. It is important to fully define the human microflora of the healthy oral cavity before we can understand the role of bacteria in oral disease.The oral cavity is comprised of many surfaces, each coated with a plethora of bacteria, the proverbial bacterial biofilm. Some of these bacteria have been implicated in oral diseases such as caries and periodontitis, which are among the most common bacterial infections in humans. For example, it has been estimated that at least 35% of dentate U.S. adults aged 30 to 90 years have periodontitis (1). In addition, specific oral bacterial species have been implicated in several systemic diseases, such as bacterial endocarditis (4), aspiration pneumonia (26), osteomyelitis in children (8), preterm low birth weight (6,20), and cardiovascular disease (2,34). Surprisingly, little is known about the microflora of the healthy oral cavity.By using culture-independent molecular methods, we previously detected over 500 species or phylotypes in subgingival plaque of healthy subjects and subjects with periodontal diseases (21), necrotizing ulcerative periodontitis in human immunodeficiency virus-positive subjects (23), dental plaque in children with rampant caries (3), noma (22), and on the tongue dorsum of subjects with and without halitosis (15). Other investigators have used similar techniques to determine the bacterial diversity of saliva (25), subgingival plaque of a subject with gingivitis (16), and dentoalveolar abs...

Two-component signal transduction systems in oral bacteria

“…These groups diverge in abundance, preferred sites of colonization, and expression of functions associated with oral and systemic infections, including dental caries, bacteraemia, and infectious endocarditis. Species that predominantly initiate colonization of the supra-gingival dental surfaces under healthy-associated conditions include the Mitis ( Streptococcus mitis and Streptococcus oralis ) and the Sanguinus groups ( Streptococcus sanguinis and Streptococcus gordonii ) [81,82]. Although S. mitis and S. sanguinis are pioneer colonizers of teeth, S. sanguinis is mostly restricted to dental surfaces, while S. mitis is abundant in a large range of mucosal and tooth sites, and may persist in significant numbers in biofilms associated with caries [83,84], a consequence of the high level of genetic heterogeneity within the species [85,86].…”

Inhibition ofSteptococcus mutansbiofilm formation by extracts ofTenacibaculumsp. 20J, a bacterium with wide-spectrum quorum quenching activity

“…Therefore, the inhibition of QS, a process known as quorum quenching (QQ), constitutes an interesting alternative for controlling pathogenic bacterial behaviours [4]. Oral biofilms comprise about 500–1,000 species, almost half of them still uncultured [5]. Among them, Streptococcus species are the initial colonizers of clean teeth surfaces and the main components of early dental plaque.…”

Contemporary perspective on plaque control

“…14 The application of cultureindependent, molecular approaches has identified about 1,200 different types of microbe that can inhabit the human mouth. 1 However, any particular mouth may contain only up to about 80 species, 15 although the application of more powerful and sensitive molecular approaches will increase this number, as species that are present only in low numbers will be detected. The Human Oral Microbiome project is underway and aims to identify and characterise all members of the resident oral microflora; 1 the conclusion of these studies will permit a more accurate description of what is the 'normal oral microflora' .…”