E-cigarettes Sculpt the Oral Microbial Landscape

Objectives: E-cigarettes or ENDS are becoming increasingly popular due to the perception that they are safe. Early research showed that ENDS deliver lower levels of toxicants typically associated with tobacco-related disease than cigarettes do, however, recent evidence has shown that e-cigarettes increase the virulence potential of the oral microbiome. The goal of the present investigation was to investigate the effect of e-cigarette vapor on the dynamics of oral bacterial colonization.
Methods: Sterilized, hydroxyapatite discs were incubated in artificial saliva for 24 hours to establish a pellicle coat, following which six pioneer were seeded and incubated aerobically. Pathogen-rich biofilms were created by further seeding the commensal biofilms with an intermediate colonizer (Fusobacterium nucleatum), followed 24 hours later by eight pathogens and incubating anaerobically. Biofilms were created under three conditions: e-cigarette vapor containing nicotine, nicotine-free e-cigarette vapor and non-vaped controls. RNA was isolated, mRNA enriched and sequenced. Microbial transcripts were quality filtered using SolexaQA++, and aligned against the Human Oral Microbiome Database (HOMD) using DIAMOND. Aligned sequences were annotated to the KEGG database using Megan6.
Results: Significant differences (Adonis, p<0.05) were observed between ENDS and control groups at all levels of biofilm development. ENDS with nicotine also demonstrated distinct differences from nicotine-free ENDS. Both nicotine-containing and nicotine-free ENDS upregulated antibiotic resistance genes in the pioneer species, while downregulating genes responsible for central metabolism. Addition of Fusobacterium nucleatum to the pioneer species in the vapor-rich environment led to downregulation of genes responsible for transcriptional activity in biofilms created intermediate biofilms that showed a downregulation in transcriptional genes. The addition of pathogen species in the vapor rich environment further decreased expression of metabolism genes.
Conclusions: E-cigarette vapor alters transcriptional activity in all stages of biofilm colonization, and can contribute to change in biofilm gene expression. This has important implications for regulating host-response and host-bacterial homeostasis.