63 FUTURE ASPECTS Recently, oral lactic Enzalutamide acid bacteria and bifidobacteria have been isolated and characterized for various oral health purposes, including caries, periodontal diseases, and halitosis.10,56,64�C68 In addition, dairy strains have been studied with the aim of characterizing potential new oral probiotics;69,70 thus, the new probiotic products targeted for oral health purposes do not necessarily comprise the same species as products now in market. Furthermore, the species might not necessarily belong only to genera Lactobacillus or Bifidobacteium. Indeed, S. salivarius K12 is used to treat oral malodor,55 and preliminary results have been published on the safety and efficacy of a probiotic mouthwash containing three different oral streptococci for reducing the number of bacteria associated with dental caries and periodontitis.
71 Genetically modified microbes bring a new dimension to the concept of probiotics. One approach is to reduce the harmful properties of pathogenic strains naturally colonizing the oral cavity. The modified strain could then be used to replace the original pathogen. One ambitious and promising example is the generation of an S. mutans strain with a complete deletion of the open reading frame of lactate hydrogenase and thus significantly reduced cariogenicity.72 Another option could be to enhance the properties of a potentially beneficial strain. One example is the construction of an L. paracasei strain with a functional scFV (single-chain variable fragment) antibody binding to the surface of Porphyromonas gingivalis.
73 Probiotics are by definition viable, and until recently the viability of probiotic bacteria was usually ascertained by culture; however, both in the intestine and in the oral cavity, a significant proportion of bacteria are not yet cultivable. In addition, bacteria in biofilms can enter a dormant state; therefore, it can be speculated that bacteria with the ability to influence the microbiota in these sites need not necessarily be culturable. There has also been debate on the definition of ��viable,�� and even whether the definition of probiotic should be changed. Indeed, heat-killed beneficial oral Streptococcus strains have been shown to exert effects similar to those of a living bacterium.74 Furthermore, viable but nonculturable probiotic bacteria maintain properties of viable bacteria.
75 SUMMARY AND CONCLUSIONS The interest in oral probiotics has been growing during the last GSK-3 decades. Most of the studies have been conducted with probiotic strains originally suggested for gut health; however, it is important to realize that each of the suggested health benefits should be studied for each bacterial strain individually. Thus, a probiotic bacterium in the mouth is not necessarily an oral probiotic. Furthermore, it is quite possible that the same species are not optimal for all oral health purposes; e.g., different properties might be desired in respect to dental and gingival health.