Molecular basis of tobacco-induced bacterial biofilms: An in vitro study

Objective. To evaluate changes in the expression of biofilmrelated genes when exposed to tobacco smoke and oxidative stress. Study Design. Experimental, in vitro. Setting. Laboratories of Rhinology and Microbiology, University of Pennsylvania. Subjects and Methods. Bacterial biofilm mass was measured using crystal violet staining and measurement of the optical density. Biofilm-related genes of the Pseudomonas aeruginosa PAO1 strain (pilF, flgK, lasI, lasB, rhlA, and algC) were studied following repetitive exposure to exogenous tobacco smoke and hydrogen peroxide. This was done using a reporter plasmid. Results. After 1 exposure to smoke, there was no change in biofilm formation. However, after 2 and 3 exposures, the biofilm formed had an increased mass (P<.05). With respect to oxidative stress in the form of H2O2, bacterial cultures demonstrated a dose- and time-dependent induction of biofilm formation compared with control conditions. Gene expression following repetitive smoke exposure demonstrated an increase in expression of pilF, flgK, algC, and lasI genes (P< .05); a decrease in rhlA (P<.05); and no significant change in the lasB gene (P = 0.1). Gene expression following H2O2 exposure demonstrated an increase in pilF (P<.05), whereas the other genes failed to demonstrate a statistical change. Conclusions. Repetitive tobacco smoke exposure leads to molecular changes in biofilm-related genes, and exposure to oxidative stress in the form of H2O2 induces biofilm growth in PAO1. This could represent adaptative changes due to oxidative stress or chemically mediated through any of the several chemicals encountered in tobacco smoke and may explain increased biofilm formation in microbes isolated from smokers.