The airways of cystic fibrosis (CF) patients with chronic Pseudomonas mTOR inhibitor aeruginosa infection represent a complex environment which shapes evolution of the bacteria (Yang et al., 2011). The complexity of the environment is due to differences in the inflammatory process and antibiotic penetration in the

different focal areas of infection which occur in the compartments of the respiratory tree: paranasal sinuses, are conductive and respiratory zones where the bacteria form biofilms (Bjarnsholt et al., 2009; Hoiby et al., 2010). The biofilm mode of growth is the main reason for the failure of antibiotic treatment to eradicate airway infection, allowing the bacteria to persist for decades in the CF lung. It has been shown that P. aeruginosa might survive in the CF lung for more than 200 000 generations, during which evolution through adaptive mutagenesis occurs (Yang et al., 2011). The biofilm mode of growth has been shown to play an important role in the evolution of bacterial diversification (Boles & Singh, 2008). Oxidative stress has been shown to trigger the diversification process both inside (Boles & Singh, 2008; Driffield et al., 2008; Conibear et al., 2009) and outside the biofilm due to inflammation and antibiotic treatment (Ciofu et al., 2005; Kohanski et al.,

2007). As a consequence of bacterial evolution in the CF airways, P. aeruginosa CF strains often exhibit remarkable phenotypic diversity, as documented from the appearance of multiple colony morphology variants, including the mucoid phenotype, the development of hypermutability AZD9291 manufacturer and various degree of antimicrobial resistance (Doggett, 1969; Hoiby, 1977; Ciofu et al., 1994; Oliver et al., 2000). It has been proposed that this diversity is associated with specialized adaptation

to the different compartments in the CF airways (Bjarnsholt et al., 2009; Hassett et al., 2010; Mowat et al., 2011). The tolerance of biofilms to antibiotics is a physiological condition that does not involve mutations in resistance genes and allows the bacteria to survive, but not necessarily grow, in the presence of antibiotic concentrations above their planktonic minimal inhibitory concentration (MIC) (Ciofu & Tolker-Nielsen, 2011). Recent research has shown that biofilm tolerance GNA12 is multifactorial, involving restricted penetration, differential metabolic/physiological activity in bacterial subpopulations of biofilms, presence of persisters and activation of biofilm-specific genes (Fux et al., 2005; Williamson et al., 2012). Here we address the question of how the antibiotic tolerance of biofilms is affected by mucoidy, hypermutability and antibiotic resistance of planktonic cells, based on in vitro investigations. A discussion of the therapeutic recommendations in light of the in vitro results is presented.