Abstract
Bacteriocin-producing probiotic Streptococcus salivarius M18 offers beneficial modulatory capabilities within the oral microbiome, apparently through potent inhibitory activity against potentially deleterious bacteria, such as Streptococcus pyogenes. The oral cavity persistence of S. salivarius M18 was investigated in 75 subjects receiving four different doses for 28 days. Sixty per cent of the subjects already had some inhibitor-producing S. salivarius in their saliva prior to probiotic intervention. Strain M18’s persistence was dependent upon the dose, but not the period of administration. Culture analysis indicated that in some individuals the introduced strain had almost entirely replaced the indigenous S. salivarius, though the total numbers of the species did not increase. Selected subjects showing either high or low probiotic persistence had their salivary populations profiled using Illumina sequencing of the V6 region of the 16S rRNA gene. Analysis indicated that while certain bacterial phenotypes were markedly modulated, the overall composition of the oral microbiome was not modified by the probiotic treatment. Megaplasmids encoding bacteriocins and adhesion factors were transferred in vitro to generate a transconjugant S. salivarius exhibiting enhanced antimicrobial production and binding capabilities to HEp-2 cells. Since no widespread perturbation of the existing indigenous microbiota was associated with oral instillation and given its antimicrobial activity against potentially pathogenic streptococci, it appears that application of probiotic strain M18 offers potential low impact alternative to classical antibiotic prophylaxis. For candidate probiotic strains having relatively poor antimicrobial or adhesive properties, unique derivatives displaying improved probiotic performance may be engineered in vitro by megaplasmid transfer.
Highlights
In the past, properties such as the impact of dose on probiotic persistence and modulation of the microbiota have been less frequently studied, as the major focus of probiotic research has been on achieving efficacious outcomes, often with the largest costeffective dosage regimen
Further analysis of this bacteriocin-like inhibitory substances (BLIS) activity using the P-typing method [20] showed that 26% of subjects had Streptococcus salivarius which produced antimicrobial substances, which inhibited at least 3/9 indicator organisms, tested
Tonsillitis, dental caries and cystic fibrosis have shown a correlation between a reduction in the levels of potential bacterial pathogens and the presence of these ‘‘antagonistic’’ streptococcal commensals within the upper respiratory tract microbiota [33,34,35,36,37,38,39,40]
Summary
Properties such as the impact of dose on probiotic persistence and modulation of the microbiota have been less frequently studied, as the major focus of probiotic research has been on achieving efficacious outcomes, often with the largest costeffective dosage regimen. Bacterial pathogens tend to have specific virulence traits that facilitate their attachment and subsequent invasion, of oral and intestinal tissue, even in the presence of a protective layer of commensal bacteria, which themselves have adapted for attachment and survival, yet, seldom do the same commensal species become established in detectable numbers when administered in probiotic formulations. This has led to the suggestion that host factors influence the persistence of a microorganism newly introduced to an already established microbial ecosystem. ‘Muller’s rachet’ theory holds that asexual organisms (in this case bacteria kept in pure culture that are not transferring or receiving DNA from their surrounding community), display genetic drift resulting in a loss of functions as a consequence of the gradual genetic decline effected by random mutation [9,10]
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