LAUSR

Tobacco smoking represents the leading preventable cause of death worldwide. Smoking is a recognised risk factor for several pathologies and is detrimental to host immune surveillance and defence. However, the impact of smoking on microbial residents of the nasopharyngeal cavity, in contact with cigarette smoke (CS), is lacking. Staphylococcus aureus is a major human pathogen which colonises the nasopharynx in 20-30% of people and can cause a wide range of infections including pneumonia. Therefore, we investigated the impact of CS on specific virulence phenotypes important in S aureus pathogenesis. We observed that CS exposure resulted in an increase in S aureus biofilm formation, invasion of and persistence within bronchial alveolar epithelial cells. Both of these CS-induced phenotypes were dependent on functional global regulatory systems (accessory gene regulator (Agr), SarA and sigmaB) and fibronectin binding-protein (FnBP) expression. Furthermore, CS exposure resulted in decreased S aureus toxin production, a prerequisite for increased intracellular persistence, and decreased susceptibility to the microbicidal free fatty acid, oleic acid, an important component of innate immunity. Importantly, exposure of S aureus to CS resulted in a greater than 16-fold increase in gentamicin-resistant small colony variant (SCV) formation, a sub-population associated with increased intracellular persistence and recurrent infections. Mutational analysis revealed that CS induced SCVs arose due to increased mutation via the SOS response DNA repair system. Taken together, our results suggests that CS redirects S aureus to a virulence phenotype associated with persistent infections.