Ethnicity-specific microbiome in early childhood caries: a functional perspective of oral biofilm

National surveillance data show persistent racial and ethnic disparities in early childhood caries (ECC), but the underlying causes of these differences have not been determined. This study examined both functional and taxonomic differences in ECC-related microbial activity between two high-risk groups of children: African American (AA) and Latin American Hispanic (LAH). Metatranscriptomic profiling of paired non-caries and caries plaque revealed consistent population-level shifts in gene expression and enabled species-level attribution of metabolically active microbes in caries lesions. A core set of well-established cariogenic organisms was consistently present and highly over-expressed in caries of both groups, including Streptococcus mutans, Veillonella parvula, Propionibacterium acidifaciens, and Lactobacillus rhamnosus. Beyond identifying the core organisms and functions active in lesions, we have also made two significant observations. First, the active communities in the two groups have substantially diverged: 4,900+ genes across 413 Kyoto Encyclopedia of Genes and Genomes Orthology (KO) groups were consistently (25%+ of samples) over-expressed in AA children, and 6,500+ genes across 382 KOs were consistently (57% of samples) over-expressed in LAH children. This reproducibility across multiple samples indicates robust group-level differences rather than random variation or single-sample effects. Second, although AA and LAH children exhibited similar functional responses to caries (sharing 1,392 KOs), these shifts were expressed by different bacterial species, indicating that distinct taxa may occupy similar metabolic niches in different groups. Taken together, these findings suggest that there is no single universal caries-associated microbiome; instead, a shared cariogenic core is necessary, but differences among the non-core taxa and their functional activity may be key to understanding ECC disparities. IMPORTANCE The disparity in tooth decay among young children has long been demonstrated in national surveillance data. While various factors including family, culture, access to health insurance, and medical infrastructure have been studied, the global transcriptomic perspective remains underexplored. Employing RNA-Seq technology, we examine functional and taxonomic differences in caries-associated microbial activity between two high-risk populations. Besides a core set of well-established cariogenic organisms, we observed significant and consistent differences in the active microbial communities between these two high-risk populations, African American (AA) and Latin American Hispanic (LAH) children. In AA children, Pseudopropionibacterium propionicum and Cardiobacterium hominis consistently showed the highest caries-related gene expression. In contrast, among LAH children, Propionibacterium acidifaciens, Selenomonas sp., Rothia dentocariosa, Atopobium parvulum, and Streptococcus sanguinis were the primary drivers of gene expression in caries lesions. By identifying the unique microbial mechanisms and pathways active in each population, we can better define the core factors required for caries development and uncover how differences in microbial function contribute to persistent disparities.