Objectives Little is known about the impact of diet on the oral microbiota of infants although diet is known to affect the gut microbiota. The aims of the present study were to compare the oral microbiota in breastfed and formula-fed infants, and investigate growth inhibition of streptococci by infant-isolated lactobacilli. Subjects and Methods 207 mothers consented to participation of their three-month old infants. 146 (70.5%) infants were exclusively and 38 (18.4%) partially breastfed, and 23 (11.1%) were exclusively formula-fed. Saliva from all infants was cultured for Lactobacillus species, with isolate identifications from 21 infants. Lactobacillus isolates were tested for their ability to supress Streptococcus mutans and Streptococcus sanguinis. Oral swabs from 73 infants were analysed by the Human Oral Microbe Identification Microarray (HOMIM) and by q-PCR for Lactobacilius gasseri. Results Lactobacilli were cultured from 27.8% of exclusively and partially breastfed infants, but not from formula-fed infants. The prevalence of 14 HOMIM detected taxa, and total salivary lactobacilli counts differed by feeding method. Multivariate modelling of HOMIM detected bacteria and possible confounders clustered samples from breastfed infants separately from formula-fed infants. The microbiota of breastfed infants differed based on vaginal or C-section delivery. Isolates of Lactobacillus plantarum, L. gasseri and Lactobacillus vaginalis inhibited growth of the cariogenic S. mutans and the commensal S. sanguinis: L. plantarum > L. gasseri > L. vaginalis. Conclusion The microbiota of the mouth differs between breastfed and formula-fed three-month-old infants. Possible mechanisms for microbial differences observed include species suppression by lactobacilli indigenous to breast milk.

BackgroundThe aim of this longitudinal study was to evaluate the oral microbiota in children from age 3 months to 3 years, and to determine the association of the presence of caries at 3 years of age.Methods and findingsOral biofilms and saliva were sampled from children at 3 months (n = 207) and 3 years (n = 155) of age, and dental caries was scored at 3 years of age. Oral microbiota was assessed by culturing of total lactobacilli and mutans streptococci, PCR detection of Streptococcus mutans and Streptococcus sobrinus, 454 pyrosequencing and HOMIM (Human Oral Microbe Identification Microarray) microarray detection of more then 300 species/ phylotypes. Species richness and taxa diversity significantly increased from 3 months to 3 years. Three bacterial genera, present in all the 3-month-old infants, persisted at 3 years of age, whereas three other genera had disappeared by this age. A large number of new taxa were also observed in the 3-year-olds. The microbiota at 3 months of age, except for lactobacilli, was unrelated to caries development at a later age. In contrast, several taxa in the oral biofilms of the 3-year-olds were linked with the presence or absence of caries. The main species/phylotypes associated with caries in 3-year-olds belonged to the Actinobaculum, Atopobium, Aggregatibacter, and Streptococcus genera, whereas those influencing the absence of caries belonged to the Actinomyces, Bergeyella, Campylobacter, Granulicatella, Kingella, Leptotrichia, and Streptococcus genera.ConclusionsThus, during the first years of life, species richness and taxa diversity in the mouth increase significantly. Besides the more prevalent colonization of lactobacilli, the composition of the overall microbiota at 3 months of age was unrelated to caries development at a later age. Several taxa within the oral biofilms of the 3-year-olds could be linked to the presence or absence of caries.

Acidogenicity and the levels of mutans streptococci (MS) in dental plaque after the use of Lactobacillus rhamnosus GG (LGG) and Lactobacillus reuteri were determined. The study had a randomised, double-blind, crossover design. Thirteen volunteers used tablets containing LGG or a combination of L. reuteri SD2112 and PTA 5289 for 2 weeks. At baseline and at the end of each tablet period, all available supragingival plaque was collected. Lactic acid production was determined from a fixed volume (8 μl) of fresh plaque and the rest of the plaque was used for culturing MS and lactobacilli. The retention of probiotics to the plaque was assessed using PCR techniques. No probiotic-induced changes were found in the acidogenicity of plaque. Also, MS counts remained at the original level. The number of subjects with lactobacilli in plaque increased in the L. reuteri group (p = 0.011) but not in the LGG group. PCR analysis of plaque revealed the presence of LGG in four and L. reuteri in six subjects after the use of the probiotic. The use of the lactobacilli did not affect the acidogenicity or MS levels of plaque. Short-term consumption of LGG and L. reuteri appeared not to influence the acidogenicity of plaque.

Background Lactobacillus spp. potentially contribute to health by modulating bacterial biofilm formation, but their effects on the overall oral microbiota remain unclear.Methods and FindingsOral microbiota was characterized via 454-pyrosequencing of the 16S rDNA hypervariable region V3-V4 after 12 weeks of daily Lactobacillus reuteri DSM 17938 and PTA 5289 consumption. Forty-four adults were assigned to a test group (n = 22) that received lactobacilli lozenges (108 CFU of each strain/lozenge) or a control group that received placebo (n = 22). Presence of L. reuteri was confirmed by cultivation and species specific PCR. Tooth biofilm samples from 16 adults before, during, and after exposure were analyzed by pyrosequencing. A total of 1,310,292 sequences were quality filtered. After removing single reads, 257 species or phylotypes were identified at 98.5% identity in the Human Oral Microbiome Database. Firmicutes, Bacteroidetes, Fusobacteria, Proteobacteria, and Actinobacteria were the most abundant phyla. Streptococcus was the most common genus and the S. oralis/S. mitis/S. mitis bv2/S. infantis group comprised the dominant species. The number of observed species was unaffected by L. reuteri exposure. However, subjects who had consumed L. reuteri were clustered in a principal coordinates analysis relative to scattering at baseline, and multivariate modeling of pyrosequencing microbiota, and culture and PCR detected L. reuteri separated baseline from 12-week samples in test subjects. L. reuteri intake correlated with increased S. oralis/S. mitis/S. mitis bv2/S. infantis group and Campylobacter concisus, Granulicatella adiacens, Bergeyella sp. HOT322, Neisseria subflava, and SR1 [G-1] sp. HOT874 detection and reduced S. mutans, S. anginosus, N. mucosa, Fusobacterium periodicum, F. nucleatum ss vincentii, and Prevotella maculosa detection. This effect had disappeared 1 month after exposure was terminated.Conclusions L. reuteri consumption did not affect species richness but induced a shift in the oral microbiota composition. The biological relevance of this remains to be elucidated.Trial RegistrationClinicalTrials.gov NCT02311218

During persistent infection, optimal expression of bacterial factors is required to match the ever-changing host environment. The gastric pathogen Helicobacter pylori has a large set of simple sequence repeats (SSR), which constitute contingency loci. Through a slipped strand mispairing mechanism, the SSRs generate heterogeneous populations that facilitate adaptation. Here, we present a model that explains, in molecular terms, how an intergenically located T-tract, via slipped strand mispairing, operates with a rheostat-like function, to fine-tune activity of the promoter that drives expression of the sialic acid binding adhesin, SabA. Using T-tract variants, in an isogenic strain background, we show that the length of the T-tract generates multiphasic output from the sabA promoter. Consequently, this alters the H. pylori binding to sialyl-Lewis x receptors on gastric mucosa. Fragment length analysis of post-infection isolated clones shows that the T-tract length is a highly variable feature in H. pylori. This mirrors the host-pathogen interplay, where the bacterium generates a set of clones from which the best-fit phenotypes are selected in the host. In silico and functional in vitro analyzes revealed that the length of the T-tract affects the local DNA structure and thereby binding of the RNA polymerase, through shifting of the axial alignment between the core promoter and UP-like elements. We identified additional genes in H. pylori, with T- or A-tracts positioned similar to that of sabA, and show that variations in the tract length likewise acted as rheostats to modulate cognate promoter output. Thus, we propose that this generally applicable mechanism, mediated by promoter-proximal SSRs, provides an alternative mechanism for transcriptional regulation in bacteria, such as H. pylori, which possesses a limited repertoire of classical trans-acting regulatory factors.