Background: The key ingredients of e-cigarettes liquid are commonly propane-1,2-diol (also
called propylene glycol) and propane-1,2,3-triol (vegetal glycerol) and their antimicrobial effects
are already established. The nicotine and flavors which are often present in e-liquids can interfere with
the growth of some microorganisms. Objective: The effect of combining these elements in e-liquids is
unknown. The aim of the study was to investigate the possible effects of these liquids on bacterial
growth in the presence or absence of nicotine and flavors.
Methods: Susceptibilities of pathogenic strains (Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas
aeruginosa, Acinetobacter baumannii, Escherichia coli, Enterococcus faecalis and Sarcina
lutea) were studied by means of a multidisciplinary approach. Cell viability and antioxidant assays
were also evaluated.
Results: All e-liquids investigated showed antibacterial activity against at least one pathogenic strain.
Higher activity was correlated to the presence of flavors and nicotine.
Discussion: In most cases, the value of minimal bactericidal concentration is equal to the value of minimal
inhibitory concentration showing that these substances have a bactericidal effect. This effect was
observed in concentrations up to 6.25% v/v. Antioxidant activity was also correlated to the presence of
flavors. Over time, the viability assay in human epithelial lung A549 cells showed a dose-dependent
inhibition of cell growth.
Conclusion: Our results have shown that flavors considerably enhance the antibacterial activity of
propane-1,2-diol and propane-1,2,3-triol. This study provides important evidence that should be taken
into consideration in further investigative approaches, to clarify the different sensitivity of the various
bacterial species to e-liquids, including the respiratory microbiota, to highlight the possible role of flavors