Related Experiment Video
Updated: Aug 18, 2026

The Synergistic Effect of Visible Light and Gentamycin on Pseudomona aeruginosa Microorganisms
Published on: July 2, 2013
Azithromycin exhibits bactericidal effects on Pseudomonas aeruginosa through interaction with the outer membrane
Yoshifumi Imamura1, Yasuhito Higashiyama, Kazunori Tomono
1Second Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki 852-8501, Japan.
Abstract:
The aim of the present study was to elucidate the effect of the macrolide antibiotic azithromycin on Pseudomonas aeruginosa. We studied the susceptibility to azithromycin in P. aeruginosa PAO1 using a killing assay. PAO1 cells at the exponential growth phase were resistant to azithromycin. In contrast, PAO1 cells at the stationary growth phase were sensitive to azithromycin. The divalent cations Mg2+ and Ca2+ inhibited this activity, suggesting that the action of azithromycin is mediated by interaction with the outer membranes of the cells, since the divalent cations exist between adjacent lipopolysaccharides (LPSs) and stabilize the outer membrane. The divalent cation chelator EDTA behaved in a manner resembling that of azithromycin; EDTA killed more PAO1 in the stationary growth phase than in the exponential growth phase. A 1-N-phenylnaphthylamine assay showed that azithromycin interacted with the outer membrane of P. aeruginosa PAO1 and increased its permeability while Mg2+ and Ca2+ antagonized this action. Our results indicate that azithromycin directly interacts with the outer membrane of P. aeruginosa PAO1 by displacement of divalent cations from their binding sites on LPS. This action explains, at least in part, the effectiveness of sub-MICs of macrolide antibiotics in pseudomonal chronic airway infection.
Related Concept Videos
Inhibitors of Bacterial Protein Synthesis
Inhibitors of Gram-positive Cell Wall Synthesis
Gene Regulation in Microbial Communities: Quorum Sensing
Combined Effects of Drugs: Synergism
Such synergistic combinations...
Mechanism of Antibiotic Resistance in MRSA
Clinical Significance of Antibiotic Resistance

