Bile effects on the Pseudomonas aeruginosa pathogenesis in cystic fibrosis patients with gastroesophageal reflux

Gastroesophageal reflux (GER) occurs in most cystic fibrosis (CF) patients and is the primary source of bile aspiration in the airway tract of CF individuals. Aspirated bile is associated with the severity of lung diseases and chronic inflammation caused by Pseudomonas aeruginosa as the most common pathogen of CF respiratory tract infections. P. aeruginosa is equipped with several mechanisms to facilitate the infection process, including but not limited to the expression of virulence factors, biofilm formation, and antimicrobial resistance, all of which are under the strong regulation of quorum sensing (QS) mechanism. By increasing the expression of lasI, rhlI, and pqsA-E, bile exposure directly impacts the QS network. An increase in psl expression and pyocyanin production can promote biofilm formation. Along with the loss of flagella and reduced swarming motility, GER-derived bile can repress the expression of genes involved in creating an acute infection, such as expression of Type Three Secretion (T3SS), hydrogen cyanide (hcnABC), amidase (amiR), and phenazine (phzA-E). Inversely, to cause persistent infection, bile exposure can increase the Type Six Secretion System (T6SS) and efflux pump expression, which can trigger resistance to antibiotics such as colistin, polymyxin B, and erythromycin. This review will discuss the influence of aspirated bile on the pathogenesis, resistance, and persistence of P. aeruginosa in CF patients.