Effect of Smoking on Subgingival Microbiome in Chronic Periodontitis: A 16S rRNA Sequencing Study

<b>Background</b>: Smoking has a detrimental effect on the periodontal condition. Smoking intensity has recently been considered as a criterion for grading periodontitis cases. However, the influence of smoking intensity on the subgingival microbial community has not been evaluated in depth. This cross-sectional analytical study aims to assess the differences in the subgingival microbiome in adult patients with chronic periodontitis and different smoking habits (heavy smokers versus moderate smokers versus non-smokers). <b>Methods</b>: Sixty patients diagnosed with chronic periodontitis were grouped according to their daily smoking intensity as follows: group I (smoke ≥ 10 cigarettes/day), group II (smoke < 10 cigarettes/day), and non-smokers (group III). For each patient, samples from subgingival plaque were harvested from the deepest three periodontal pockets, and their 16S rRNA was sequenced using the S5 Ion Torrent platform. Sequences were clustered in taxonomic units, and the microbial diversity was expressed using the Shannon index or Simpson index, while the abundance of the microbial species was expressed using the Chao index. <b>Results</b>: Bacterial diversity was lowest in the heavy smoker group (group I) and highest in non-smokers (group III). <i>Veillonella</i>, <i>Streptococcus</i>, <i>Prevotella</i>, <i>Fusobacterium</i>, and <i>Dialister</i> were found to have different prevalences in the three study groups. <i>Campylobacter</i> decreased and <i>Fusobacterium</i> increased as a function of the number of cigarettes smoked per day. The moderate smoker group showed a higher abundance of <i>Spirochaetes.</i> At the species level, the heavy smoker group (group I) showed a higher abundance of <i>Fusobacterium</i> compared to the other two groups. <b>Conclusions</b>: Greater smoking intensity has been associated with higher <i>Fusobacterium</i> abundance, together with decreased diversity of the subgingival microbiome, establishing a more stable putative subgingival bacterial environment.