title: Impact of Azithromycin on the Quorum Sensing-Controlled Proteome of Pseudomonas aeruginosa.
abstract: The macrolide antibiotic, azithromycin (AZM), has been reported to improve the clinical outcome of cystic fibrosis patients, many of whom are chronically-infected with Pseudomonas aeruginosa. However, the highest clinically-achievable concentrations of this drug are well-below the minimum inhibitory concentration for P. aeruginosa, raising the question of why AZM exhibits therapeutic activity. One possibility that has been raised by earlier studies is that AZM inhibits quorum sensing (QS) by P. aeruginosa. To explicitly test this hypothesis the changes brought about by AZM treatment need to be compared with those associated with specific QS mutants grown alongside in the same growth medium, but this has not been done. In this work, we used quantitative 2D-difference gel electrophoresis and 1H-NMR spectroscopy footprint analysis to examine whether a range of clinically-relevant AZM concentrations elicited proteomic and metabolomic changes in wild-type cultures that were similar to those seen in cultures of defined QS mutants. Consistent with earlier reports, over half of the AZM-induced spot changes on the 2D gels were found to affect QS-regulated proteins. However, AZM modulated very few protein spots overall (compared with QS) and collectively, these modulated proteins comprised only a small fraction (12-13%) of the global QS regulon. We conclude that AZM perturbs a sub-regulon of the QS system but does not block QS per se. Reinforcing this notion, we further show that AZM is capable of attenuating virulence factor production in another Gram-negative species that secretes copious quantities of exoenzymes (Serratia marcescens), even in the absence of a functional QS system.
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.|Cancer Research UK Cambridge Institute, Li Ka Shing Centre, Robinson Way, Cambridge, CB2 0RE, United Kingdom.
authors.forename: J E
authors.initials: JE
authors.lastname: Swatton
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.|Department of Pathology, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
authors.forename: P W
authors.initials: PW
authors.lastname: Davenport
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.
authors.forename: E A
authors.initials: EA
authors.lastname: Maunders
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.|MRC Human Nutrition Research, Elsie Widdowson Laboratory, 120 Fulbourn Road, Cambridge, CB1 9NL, United Kingdom.
authors.forename: J L
authors.initials: JL
authors.lastname: Griffin
authors.affiliation: Cambridge Centre for Proteomics, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.
authors.forename: K S
authors.initials: KS
authors.lastname: Lilley
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Welch
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017963:Azithromycin / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D005453:Fluorescence; D005798:Genes, Bacterial; D055432:Metabolomics; D020543:Proteome; D066244:Proton Magnetic Resonance Spectroscopy; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D053038:Quorum Sensing / Q000187:drug effects* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D020543:Proteome; D017963:Azithromycin