Novel probiotics for oral diseases

The oral administration of bacteria such as lactobacilli and bifidobacteria as probiotics for the promotion and / or maintenance of gastrointestinal health is now well established. The benefits include reduction of the permeability of the gut mucosa, competition for binding sites with pathogens and reduction of inflammatory immune responses. The oral diseases dental caries and periodontal diseases are the commonest bacterial diseases of man and result from a breakdown in the normal homeostasis between the human host and its commensal microbiota. Environmental, dietary and other factors can negatively affect the balance of the oral microbiota resulting in increased numbers of bacteria associated with each disease such as Streptococcus mutans for dental caries and Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia for periodontal disease. The possible benefits to oral disease of using probiotics have been investigated and there is limited evidence to suggest that the use of products containing lactobacilli or bifidobacteria may reduce the numbers of both Streptococcus mutans and some anaerobic bacteria, including those associated with periodontitis. However, a weakness of this approach is that lactobacilli and bifidobacteria can be cariogenic themselves and although they may replace S. mutans in carious lesions, the cariogenicity of the lesion may not be reduced. Specific oral probiotics such as Streptococcus salivarius, a commensal oral organism, have been evaluated with some beneficial effects observed but no systematic search for suitable oral species, based on a detailed knowledge of oral microbial ecology, has been performed. In order to develop a probiotic approach for oral diseases, it is first necessary to identify those bacterial species and consortia specifically associated with health. Perhaps unsurprisingly, most cultural and non-cultural bacterial community based studies have focused on disease. In this study, a comprehensive analysis of the microbiota associated with oral health will be performed. Samples will be cultured using non-selective media incubated aerobically and anaerobically. Isolates will be identified by sequence analysis of appropriate housekeeping genes, principally that encoding the 16S rRNA. In addition, DNA will be extracted directly from the samples and 16S rRNA genes amplified by PCR, cloned and sequenced. Isolates and clones will be identified with reference to the Human Oral Microbiome Database (www.homd.org) of which Professor Wade is a curator. In order to exclude organisms found in both health and disease, further samples from healthy subjects and those with dental caries and periodontal disease will be collected and the Human Microbe Identification Array (Forsyth Institute, Boston) used to identify organisms specifically associated with health and not found in carious lesions or sites of gingival inflammation. In this way, A panel of oral health-associated bacterial strains will be established. Candidate organisms will then be screened for their ability to inhibit the growth of disease-associated organisms by means of both classical bacteriocin / microcin assays. The ability of strains to block the adherence of dental plaque pioneer species to saliva-coated enamel will be determined and In-vitro biofilm models will be used to assess if strains are able to displace oral disease-associated species from established biofilms. Strains will also be screened for undesirable characteristics such as resistance to commonly used antimicrobials and the production of virulence factors such as proteolytic enzymes with the capability of degrading substrates found in oral tissues. This study will enable a panel of oral bacterial strains with the potential for use as oral probiotics to be established, based on an understanding of the microbial ecology of oral health, which hitherto has not been available.