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

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.

Flavorless vs. Flavored Electronic Cigarette-Generated Aerosol and E-Liquid on the Growth of Common Oral Commensal Streptococci

“…In the first experiment, the effect of 100 puffs of ECIG-generated aerosol were compared to the effect of 1% stock E-liquid ± low concentration (0.05% final percentages in BHI) flavorings, while the second experiment tested for dose responses using stock flavorless E-liquid or E-liquids with low concentration or high concentration flavorings Table 2. As shown in Figure 1, fresh, sterile BHI media (10 ml in 50 ml plastic conical tubes) were supplemented with 1, 1.25, 2.5, or 5% E-Liquid ± low or high concentration flavorings and stored overnight in the refrigerator (4 • C), following the methodology of Nelson et al (2019), which reports no profound differences in the overall growth kinetics of three of the four species tested. Moreover, in order to make our experiments more physiologically relevant, the percentages of stock E-liquid ± flavorings chosen were based on calculations determined from a hypothetical open-system model as outlined in Table 3.…”

“…One hundred 5-sec puffs of the E-liquid represents about 1% E-liquid in BHI. A portion of this figure is adapted from Nelson et al (2019). were incubated at 37 • C and 5% CO 2 for the duration of the experiment, except for the short period of time it took to obtain the absorbance readings.…”

“…As previously described (Nelson et al, 2019), E-liquid was aerosolized using a Tripl3 (Kennesaw, GA, United States) eGo style lithium ion battery (650 mAh, 3.7 V unregulated). The E-liquid was housed in a 1.8 mL capacity Aspire glass tank (Shenzhen Eigate Technology Co., Ltd., Shenzhen, China) equipped with a 1.8 resistance coil for an average power output of ≈ 7.6 W. Air or ECIG-generated aerosol ± flavorings were delivered into 10 ml of BHI using a Cole-Palmer Master Flex L/S peristaltic pumps (Vernon Hills, IL, United States).…”

“…Using this methodology, 9.3 µL of E-liquid is aerosolized per puff, or 930 µL for 100 puffs (Palazzolo et al, 2017). Since it was determined that the percent recovery of aerosolized E-liquid in the BHI is between 8.4 and 10.1% (Nelson et al, 2019), the amount of aerosolized E-liquid that is present in the BHI ranges between 78 and 94 µL. Consequently, 100 µL of E-liquid added directly to the 10 ml of BHI (or 1%) is roughly equivalent to 100 puffs.…”

“…A recent study demonstrates a significant shift in the beta-diversity of the oral microbiota in ECIG users (Pushalkar et al, 2020). Previous studies from our group have explored the effects of flavorless ECIG aerosol with and without nicotine, and reported that ECIG aerosols have a less detrimental effect on the survival and growth of oral commensal streptococci than conventional cigarette smoke (Cuadra et al, 2019;Nelson et al, 2019), albeit the effects of flavorings were not explored.…”