Electronic Cigarette (E-Cigarette) Vapor Exposure Alters the Streptococcus pneumoniae Transcriptome in a Nicotine-Dependent Manner without Affecting Pneumococcal Virulence.

The effects of electronic cigarette (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 the virulence and transcriptome of Streptococcus pneumoniae strain TIGR4, a pathogen that asymptomatically colonizes the human nasopharyngeal mucosa. TIGR4 was preexposed for 2 h to nicotine-containing EV extract (EVE+NIC), nicotine-free EV extract (EVE-NIC), cigarette smoke extract (CSE), or nutrient-rich tryptic soy (TS) broth (control). The differences between the treatment and control strains were explored using transcriptome sequencing (RNA sequencing [RNA-Seq]), in vitro virulence assays, and an in vivo mouse model of acute pneumonia. The analysis of RNA-Seq profiles revealed modest changes in the expression of 14 genes involved in sugar transport and metabolism in EVE-NIC-preexposed TIGR4 compared to the control, while EVE+NIC 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 preexposed 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 EVE-NIC) 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 S. pneumoniae transcriptome in a nicotine-dependent manner without affecting pneumococcal virulence.IMPORTANCE With the increasing popularity of e-cigarettes among cigarette smoking and nonsmoking adults and children and the recent reports of vaping-related lung illness and deaths, further analysis of the adverse health effects of e-cigarette vapor (EV) exposure is warranted. Since pathogenic bacteria such as Streptococcus pneumoniae can colonize the human nasopharynx as commensals, they may be affected by exposure to bioactive chemicals in EV. Hence, in this study we examined the effects of EV exposure on the physiology of S. pneumoniae strain TIGR4. In order to differentiate between the effects of nicotine and nonnicotine components, we specifically compared the RNA-Seq profiles and virulence of TIGR4 exposed to vapor from nicotine-containing and nicotine-free e-liquid formulations. We observed that nicotine-containing EV augmented TIGR4 biofilms and altered expression of TIGR4 genes predominantly involved in metabolism and stress response. However, neither nicotine-containing nor nicotine-free EV affected TIGR4 virulence in a mouse model.