[Differences in Oral and Gut Microbiome Composition Among Preschool Children in Urumqi During the Deciduous and Mixed Dentition Periods].

Microbial richness and evenness differed significantly between the oral cavity and intestine in preschool children.

• 16S rRNA gene-based third-generation sequencing was used to analyze saliva and fecal samples.
• Sample size was 10 children with deciduous dentition and 10 with mixed dentition.
• The differences in microbial richness (Chao1 index) and evenness (Shannon index) between the oral cavity and intestine were statistically significant (P = 0.001).

Firmicutes, Proteobacteria, and Bacteroidetes were the three dominant phyla in both oral and gut microbiota across both dentition stages.

• These three phyla were dominant at both the oral and gut sites regardless of dentition stage.
• At the genus level, Neisseria and Streptococcus were abundant in the oral cavity.
• Bacteroides and Faecalibacterium predominated in the gut.

o_Lactobacillales was identified as the marker taxon in the oral cavity during the deciduous dentition period.

• LDA score = 5.04, P < 0.001.
• This finding was based on LEfSe (Linear Discriminant Analysis Effect Size) analysis.
• This marker distinguished the oral microbiota of deciduous dentition children from mixed dentition children.

g_Neisseria was identified as the oral marker genus in children with mixed dentition.

• LDA score = 5.15, P < 0.001.
• This genus was enriched in the oral microbiota specifically during the mixed dentition period.
• The shift from Lactobacillales dominance to Neisseria dominance indicates a change in oral microbial composition as dentition transitions.

Gut marker genera during the deciduous dentition period included o_Bacteroides and f_Lachnospiraceae.

• o_Bacteroides had LDA = 5.17, P < 0.001.
• f_Lachnospiraceae had LDA = 5.16, P < 0.001.
• These taxa were identified as enriched in the gut microbiota specifically during the deciduous dentition stage.

Gut marker genera during the mixed dentition period included f_Ruminococcaceae and g_Faecalibacterium.

• f_Ruminococcaceae had LDA = 5.09, P < 0.001.
• g_Faecalibacterium had LDA = 5.03, P < 0.001.
• These taxa were enriched in the gut microbiota specifically during the mixed dentition stage, indicating a shift in gut microbial composition with changing dentition.

Oral and gut microbiota differed in their predicted metabolic functional pathways.

• Upregulation of pathways including lactose degradation and nitrate reduction was observed in the oral microbiota.
• In contrast, the gut microbiota showed enhanced activity of the methanogenesis from acetate pathway.
• These functional differences suggest distinct metabolic roles for oral versus gut microbial communities in preschool children.