Microbiological Assessment of Halitosis in Users of E-Cigarettes, Heated Tobacco Products, and Combustible Cigarettes

Background/Objectives: The diagnostic value of oral microbiological testing in users of different nicotine products remains uncertain. We compared tongue-coating dysbiosis, salivary cultures, and chairside enzymatic activity across product groups and evaluated their discrimination of objective halitosis. Methods: This cross-sectional study included 225 adults: 60 never-users, 55 combustible cigarette users, 52 heated tobacco product users, and 58 e-cigarette users. Six tongue-coating taxa and total bacterial load were quantified by quantitative polymerase chain reaction. Salivary cultures and the benzoyl-DL-arginine-naphthylamide (BANA) test complemented organoleptic assessment and volatile sulfur compound measurement. Analyses included adjusted regression, compositional analysis, exploratory profiling and mediation, and receiver operating characteristic analysis. Results: Adjusted dysbiosis-index differences versus never-users were 1.82, 1.50, and 2.08 units for combustible cigarette, heated tobacco product, and e-cigarette users, respectively (all p < 0.001). E-cigarette users had the highest Solobacterium moorei load and Candida carriage, whereas combustible cigarette users had the highest Porphyromonas gingivalis load and BANA positivity. Permutational multivariate analysis of variance (PERMANOVA) R2 was 15.8%, with heterogeneous dispersions. Objective halitosis prevalence ranged from 10.8% to 66.7% across microbial profiles. The chairside/culture panel and dysbiosis index had areas under the curve of 0.72 and 0.71, respectively. Conclusions: Microbial differences were associated with product use, but exposure history and oral conditions may confound these associations. Moderate discrimination and absent external validation preclude diagnostic interchangeability or routine implementation of these adjunctive tests.