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Comparative Study
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A Comparison of Flavorless Electronic Cigarette-Generated Aerosol and Conventional Cigarette Smoke on the Planktonic Growth of Common Oral Commensal Streptococci

Affiliations
Comparative Study

A Comparison of Flavorless Electronic Cigarette-Generated Aerosol and Conventional Cigarette Smoke on the Planktonic Growth of Common Oral Commensal Streptococci

John M Nelson et al. Int J Environ Res Public Health.

Abstract

Background: Smoking is the number one predictor for the development of periodontal disease. Consequently, electronic cigarette (ECIG) use has prompted investigations into the health-related risks induced by ECIG-generated aerosol on oral commensal bacteria as compared to cigarette smoke. Since E-liquid contains fewer constituents than smoke, we hypothesize that growth media containing E-liquid or aerosol has less impact on oral commensal streptococci than cigarette smoke. Methods: Eight-hour growth curves were generated for three strains of streptococci following exposure of growth media to nicotine alone (0.05, 0.1, 0.2 mg/mL), E-liquid ± nicotine (2.3, 4.7, 7.0 µL/mL), ECIG-generated aerosol ± nicotine (25, 50, 75 puffs), or cigarette smoke (2, 5, 10, 25, 50, 75 puffs). Nicotine and E-liquid were added to the media at concentrations equivalent to vaporized amounts of 25, 50, or 75 puffs. Absorbance readings were taken at 0, 2, 4, 6, and 8 h of bacterial growth. Results: Both E-liquid and aerosol (±nicotine) had little to no effect on eight-hour streptococcal growth. In contrast, five puffs of smoke inhibited streptococcal growth. Conclusions: Smoke-treated growth media, but not E-liquid or ECIG-generated aerosol, inhibits the growth of oral commensal streptococci. A possible implication is that aerosol may induce less periodontitis than smoke.

Keywords: E-liquid; ECIG; aerosol; oral commensal bacteria; smoking; streptococci; vaping.

Conflict of interest statement

The authors declare that this manuscript was written without any commercial or financial relationships that could be misconstrued as potential conflict of interest.

Figures

Figure 1
Figure 1
Schematic of the exposure apparatus for flavorless electronic cigarette (ECIG) aerosol and cigarette smoke.
Figure 2
Figure 2
Nicotine concentration in brain heart infusion (BHI) after trapping 25, 50, and 75 puffs of aerosol or smoke. Circles = individual data points; solid line = linear regression; dotted lines = 95% confidence intervals.
Figure 3
Figure 3
Eight-hour control growth curves. Each point represents mean ± standard error of the means (SEM).
Figure 4
Figure 4
Effects of nicotine on eight-hour control growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM.
Figure 5
Figure 5
Effects of E-liquid without nicotine (on left) and with nicotine (on right) on eight-hour growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM.
Figure 6
Figure 6
Effects of air on eight-hour control growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM.
Figure 7
Figure 7
Effects of ECIG-generated aerosol without nicotine (on left) and with nicotine (on right) on eight-hour growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM.
Figure 8
Figure 8
Effects of smoke on eight-hour growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM. Linear regression analysis indicates that if the overall slopes were identical, there is less than a 0.01% chance of randomly choosing data points with slopes this different (p < 0.0001).
Figure 9
Figure 9
Effects of E-liquid composition (on left) and E-liquid aerosol composition (on right) on eight-hour growth curves and linear regression of the exponential growth phase. Each point represents mean ± SEM.
Figure 10
Figure 10
Effects of components of E-liquid (on left) or ECIG-generated aerosol (on right) on biofilm biomass. Each bar represents mean ± SEM, n = 12. The red line across each graph represents the upper 95% confidence interval of the BHI (control).
Figure 11
Figure 11
Effects of E-liquid, ECIG-generated aerosol, and smoke on biofilm formation. Representative images of biofilms shown for commensal streptococci following the addition of 0 µL E-liquid (control) or 70 µL of E-liquid (±nicotine) to 10 mL of BHI. Final concentration of E-liquid = 0.0 or 7.0 µL/mL BHI, respectively. Seventy-five puffs on an ECIG generates approximately 700 µL of aerosolized E-liquid, of which only 10 % (or 70 µL) is trapped in 10 mL of BHI. Representative biofilms also shown for streptococci following BHI exposure to 0 puffs (control) or 75 puffs of air (control), ECIG-generated aerosol (±nicotine), and smoke. All SEM images were acquired at magnification of 1500 times using an acceleration voltage of 15 kV.

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