The effects of e-cigarette vapor exposure on the transcriptome and virulence of Streptococcus pneumoniae

The effects of e-cigarette vapor (EV) exposure on the physiology of respiratory microflora are not fully defined. We analyzed the effects of exposure to vapor from nicotine-containing and nicotine-free e-liquid formulations on virulence and transcriptome of strain TIGR4, a pathogen that asymptomatically colonizes human nasopharyngeal mucosa. TIGR4 was pre-exposed for 2h to nicotine-containing EV extract (EVE), nicotine-free EV extract (EVE), cigarette smoke extract (CSE), or nutrient-rich TS broth (control). The differences in the treatment and control TIGR4 were explored using transcriptome sequencing, virulence assays, and mouse model of acute pneumonia. The analysis of RNASeq profiles revealed modest changes in the expression of 14 genes involved in sugar transport and metabolism in EVE pre-exposed TIGR4 compared to the control. While, EVE or CSE exposure altered expression of 264 and 982 genes, respectively, most of which were involved in metabolism and stress response. Infection in a mouse model of acute pneumonia with control TIGR4 or with TIGR4 pre-exposed to EVE, EVE, or CSE did not show significant differences in disease parameters, such as bacterial organ burden and respiratory cytokine response. Interestingly, TIGR4 exposed to CSE or EVE (but not EVE) exhibited moderate induction of biofilm formation. However, none of the treatment groups showed significant alterations in pneumococcal hydrophobicity or epithelial cell adherence. In summary, our study reports that exposure to EV significantly alters the transcriptome in a nicotine-dependent manner without affecting pneumococcal virulence.