**4. Cigarette smoke versus e‐cigarette vapor**

These data provide suggestive evidence that EV induces pro‐virulent changes in MRSA comparable in type and magnitude to those promoted by exposure to conventional CS. Both EV and CS exposures resulted in shifts toward more hydrophobic and less anionic surface charges, with increased adherence and invasion of epithelial cells, and resistance to killing by the AMP LL‐37. Additionally, the phenotypic changes induced by exposure to both inhalants result in significantly increased virulence in a mouse pneumonia model. Without running assays in parallel, however, definitive comparisons cannot be made (**Table 1**).

Both CS and EV exposure result in a similar profile based on these assays, likely reflecting a general stress response. However, the primary component of the inhalants inducing these


**Table 1.** Comparison of the effects of cigarette smoke and e‐cigarette vapor on MRSA pathogenicity factors and virulence.

phenotypic changes may be different. This likely reflects that CS contains a multitude of toxic chemicals, with a more limited range found in EV. However, both nicotine and degradation products of the e‐cigarette liquid solvents are clearly sufficient to induce concerning changes in MRSA *in vitro*. The effects of both CS and EV on MRSA in a physiologic setting may be synergistically negative due to the interplay of increased virulence with immunosuppressive effects of these substances on airway cells. Current studies are limited to animal models, and more research must be carried out to evaluate whether these changes reflect those observed following physiologic exposure in human users of both conventional and e‐cigarettes. Additional avenues of research include evaluating the effects of exposure to these substances on staphylococcal soft tissue infections and bacteremia. In addition, epidemiologic studies on the incidence of staphylococcal infections in e‐cigarette users are needed to assess the likelihood of our findings having a physiologic correlate.

virulence factors after EV exposure was evaluated. Panton‐Valentine leukocidin (*pvl*), α‐ hemolysin (*hla*), coagulase (*coa*), α‐phenol soluble modulin (*psm‐α*), intracellular adhesion (*icaA*), staphylococcal protein A (*spa*), and quorum sensing (*agrA*) were quantified relative to 16s rRNA as a housekeeping gene. After EV exposure, the expression of *coa* and *pvl* increased by 1.68‐ and 1.56‐fold, respectively [29]. Expression of *spa* did not change with EV exposure

These data provide suggestive evidence that EV induces pro‐virulent changes in MRSA comparable in type and magnitude to those promoted by exposure to conventional CS. Both EV and CS exposures resulted in shifts toward more hydrophobic and less anionic surface charges, with increased adherence and invasion of epithelial cells, and resistance to killing by the AMP LL‐37. Additionally, the phenotypic changes induced by exposure to both inhalants result in significantly increased virulence in a mouse pneumonia model. Without running assays in parallel, however, definitive comparisons cannot be made

Both CS and EV exposure result in a similar profile based on these assays, likely reflecting a general stress response. However, the primary component of the inhalants inducing these

**Cigarette smoke E‐cigarette vapor**

Growth ↓↓ \*\*\* ↓↓ \*\*\*\* Hydrophobicity ↑↑ \*\*\*\* ↑ \* Adherence ↑ \* ↑↑ \*\* Invasion ↑↑ \*\* ↑↑ \* Surface charge changes ++++ \*\*\*\* + \*\*\*\*

Antimicrobial peptide (AMP) ↑↑ \* ↑ \*

Biofilm formation ↑↑ \*\* Virulence *in vivo* ↑↑ \* ↑ \*

**Table 1.** Comparison of the effects of cigarette smoke and e‐cigarette vapor on MRSA pathogenicity factors and virulence.

while *icaA, agrA, hla,* and *psm* decreased.

112 Frontiers in Frontiers in Staphylococcus Aureus *Staphylococcus aureus*

(**Table 1**).

*Resistance to killing by:*

\**p* < 0.05. \*\**p* < 0.01. \*\*\**p* < 0.001. \*\*\*\**p* < 0.0001.

Macrophage ↑↑↑↑ \*\*\*\*

Cell lysis ↓ \*\*\*

**4. Cigarette smoke versus e‐cigarette vapor**

Comparison of the effects of cigarette smoke and e‐cigarette vapor on MRSA pathogenicity factors and virulence.
