Influence of heat-non-burn tobacco aerosol on the microbiome of biofilm from human whole saliva bacteria in vitro

Objectives The heat-not-burn tobacco product IQOS (I Quit Ordinary Smoking) has recently become widely used. However, the impact of IQOS aerosol on the oral microbiome remains unclear. The present study therefore aimed to investigate the influence of IQOS aerosol on the microbial composition of microcosm biofilms formed from human saliva using a standardized biofilm reactor. Material and methods A custom-designed biofilm reactor was constructed to enable the intermittent exposure of biofilms to IQOS aerosol. Microcosm biofilms were formed on bovine enamel samples with a defined surface (19.635 mm 2 ) with unstimulated pooled human saliva from three healthy probands being used as inoculum. Biofilm formation took place with continuous nutrient medium supply for 5 days. The biofilm in the test setup was exposed to IQOS aerosol 8 times a day for 5 min each time. A parallel test setup ensured simultaneous biofilm formation without exposure to IQOS aersol and served as a negative control. After 5 days, the microbial composition of the formed biofilms was examined by amplicon sequencing using the V1-V3 region of the 16S rRNA gene. In addition, the biofilm was visualized using scanning electron microscopy. Results After one week, the surfaces of the bovine enamel samples on which biofilm formation took place were similarly covered, whether under the influence of IQOS aerosol or in the negative control. The Simpson index showed significant differences ( P < 0.05), while the Pielou index showed highly significant differences (0.01 < P < 0.05), as did the Shannon index (0.001 < P < 0.01) and the Richness index ( P < 0.001). The β-diversity showed different clustering between the treated biofilm and the negative control, corresponding to the significantly different ( p = 0.001) microbial community caused by the IQOS aerosol. The abundance of the genera Gemella , Haemophilus , Neisseria and Rothia was significantly lower in biofilms influenced by IQOS aerosol. Additionally, the abundance of different species was significantly modified by IQOS aerosol. Conclusions IQOS aersol may shift oral microbial composition, even though not inhibiting biofilm growth. This highlights the need for further research into the effects on oral microbal ecology of IQOS users, as well as the development of prevention and education measures regarding the potential health risks associated with IQOS.