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 virulence and transcriptome of Streptococcus pneumoniae strain TTGR4, a pathogen that asymptomatically colonizes human nasopharyngeal mucosa effects following exposure to vapor from nicotine-containing and nicotine-free e-liquid formulations. TIGR4 was pre-exposed for 2h to nicotine-containing EV extract (EVE+NIC), nicotine-free EV extract (EVE-NIC), cigarette smoke extract (CSE), or nutrient-rich TS broth (control). The differences in the treatment and control TIGR4 were explored using transcriptome sequencing, in vitro virulence assays, and infection of 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-NIC pre-exposed TIGR4 compared to the control. While, EVE+NIC or CSE exposure altered expression of 264 and 982 genes, respectively, most were those involved in metabolism and stress response. Infection of a mouse model of acute pneumonia with control TIGR4 or with TIGR4 pre-exposed to EVE+NIC, EVE-NIC, 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+NIC (but not CSE-NIC) exhibited moderate induction of biofilm formation. However, none of the treatment groups showed significant alterations in pneumococcal hydrophobicity or epithelial cell adherence. In this study comparing the effects of acute exposure to nicotine-containing EV and nicotine-free EV on a respiratory pathogen, we report that EV significantly alters S. pneumoniae transcriptome in nicotine-dependent manner without affecting pneumococcal virulence.