title: Azithromycin blocks quorum sensing and alginate polymer formation and increases the sensitivity to serum and stationary-growth-phase killing of Pseudomonas aeruginosa and attenuates chronic P. aeruginosa lung infection in Cftr(-/-) mice.
abstract: The consequences of O-acetylated alginate-producing Pseudomonas aeruginosa biofilms in the lungs of chronically infected cystic fibrosis (CF) patients are tolerance to both antibiotic treatments and effects on the innate and the adaptive defense mechanisms. In clinical trials, azithromycin (AZM) has been shown to improve the lung function of CF patients. The present study was conducted in accordance with previous in vitro studies suggesting that the effect of AZM may be the inhibition of alginate production, blockage of quorum sensing (QS), and increased sensitivity to hydrogen peroxide and the complement system. Moreover, we show that AZM may affect the polymerization of P. aeruginosa alginate by the incomplete precipitation of polymerized alginate and high levels of readily dialyzable uronic acids. In addition, we find that mucoid bacteria in the stationary growth phase became sensitive to AZM, whereas cells in the exponential phase did not. Interestingly, AZM-treated P. aeruginosa lasI mutants appeared to be particularly resistant to serum, whereas bacteria with a functional QS system did not. We show in a CF mouse model of chronic P. aeruginosa lung infection that AZM treatment results in the suppression of QS-regulated virulence factors, significantly improves the clearance of P. aeruginosa alginate biofilms, and reduces the severity of the lung pathology compared to that in control mice. We conclude that AZM attenuates the virulence of P. aeruginosa, impairs its ability to form fully polymerized alginate biofilms, and increases its sensitivity to complement and stationary-phase killing, which may explain the clinical efficacy of AZM.
authors.affiliation: Department of Clinical Microbiology, Rigshospitalet, Institute for Medical Microbiology and Immunology, Panum Institute 24.1, University of Copenhagen, DK-2100, Copenhagen, Denmark. nadinehof@hotmail.com
authors.forename: Nadine
authors.initials: N
authors.lastname: Hoffmann
authors.forename: Baoleri
authors.initials: B
authors.lastname: Lee
authors.forename: Morten
authors.initials: M
authors.lastname: Hentzer
authors.forename: Thomas Bovbjerg
authors.initials: TB
authors.lastname: Rasmussen
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Song
authors.forename: Helle Krogh
authors.initials: HK
authors.lastname: Johansen
authors.forename: Michael
authors.initials: M
authors.lastname: Givskov
authors.forename: Niels
authors.initials: N
authors.lastname: Høiby
mesh_terms: D000464:Alginates / Q000378:metabolism*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000891:Anti-Infective Agents, Local / Q000494:pharmacology; D017963:Azithromycin / Q000494:pharmacology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008171:Lung Diseases / Q000188:drug therapy* / Q000382:microbiology* / Q000473:pathology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D053038:Quorum Sensing / Q000187:drug effects*; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D000464:Alginates; D000900:Anti-Bacterial Agents; D000891:Anti-Infective Agents, Local; D037521:Virulence Factors; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D017963:Azithromycin; D006861:Hydrogen Peroxide