Impact of Azithromycin on the Quorum Sensing-Controlled Proteome of Pseudomonas aeruginosa

• Published in: PloS one 2016-01, Vol.11 (1), p.e0147698-e0147698
• Main Authors: Swatton, J E, Davenport, P W, Maunders, E A, Griffin, J L, Lilley, K S, Welch, M
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Antibiotics; Azithromycin; Azithromycin - pharmacology; Bacteria; Bacterial Proteins - metabolism; Biochemistry; Biofilms; Biology and Life Sciences; Comparative analysis; Complications and side effects; Cystic fibrosis; Dosage and administration; Electrophoresis, Gel, Two-Dimensional; Fibrosis; Fluorescence; Footprint analysis; Gel electrophoresis; Gels; Genes, Bacterial; Genetic aspects; Health aspects; Laboratories; Magnetic resonance spectroscopy; Medical research; Medicine and Health Sciences; Metabolomics; Minimum inhibitory concentration; Mutants; NMR spectroscopy; Nosocomial infections; Nutrition research; Pathogens; Peptides; Physiological aspects; Proteins; Proteome; Proton Magnetic Resonance Spectroscopy; Pseudomonas aeruginosa; Pseudomonas aeruginosa - drug effects; Pseudomonas aeruginosa - genetics; Pseudomonas aeruginosa - metabolism; Pseudomonas aeruginosa - physiology; Quorum sensing; Quorum Sensing - drug effects; Quorum Sensing - genetics; Spectroscopy; Tennis; Virulence; Virulence factors
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0147698

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.