Tongue microbiome of smokeless tobacco users

Abstract Background: The possibility that smokeless tobacco may contribute to oral carcinogenesis by influencing the oral microbiome has not been explored. This cross sectional study sought to assess the effect of using hammah, a form of smokeless tobacco prevalent in Arabia, on the tongue microbiome. Tongue scarping samples were obtained from twenty-nine shammah users (SU; 27.34±6.9 years) and 23 shammah non-users (SNU; 27.7±7.19 years) and analyzed with 16S rRNA gene sequencing (V1-V3). Species-level taxonomy assignment of the high-quality, merged reads was obtained using a previously described BLASTn-based algorithm. Downstream analyses were performed with QIIME, LEfSe, and R. Results: A total of 178 species, belonging to 62 genera and 8 phyla were identified. Genera Streptococcus , Leptotrichia , Actinomyces , Veillonella , Haemophilus , Prevotella and Neisseria accounted for more than 60% of the average microbiome. There were no differences between the two groups in species richness and alpha-diversity, but PCoA showed significant separation (P=0.015, ANOSIM). LEfSe analysis identified 22 species to be differentially abundant between the SU and SNU. However, only 7 species maintained a false discovery rate of ≤ 0.2 and could cluster the two groups separately: Rothia mucilaginosa , Streptococcus sp. oral taxon 66, Actinomyces meyeri , Streptococcus vestibularis Streptococcus sanguinis and a potentially novel Veillonella species in association with SU, and Oribacterium asaccharolyticum with SNU. Conclusion: Shammah use induces tongue microbiome changes that may be relevant to oral carcinogenesis, namely enrichment of species with high acetaldehyde production potential, which warrants further investigation.