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In vitro activity of macrolides against intracellular Legionella pneumophila
Abstract:
The antibacterial effects of clarithromycin, azithromycin, and erythromycin were determined against five strains of Legionella pneumophila including L. pneumophila ATCC 33823 and four clinical isolates. Extracellular minimum inhibitory concentrations (MICs) and MBCs were determined by a microdilution method. Clarithromycin was the most active drug (MIC < or = 0.015-0.06), followed by azithromycin (MIC 0.03-0.12) and erythromycin (MIC 0.06-0.25). The antibacterial effect of these macrolides was then determined against L. pneumophila grown intracellularly in MRC-5 human fetal lung fibroblast cells. At two and eight times the extracellular MBC, erythromycin, azithromycin, and clarithromycin were equally effective in inhibiting growth of these five strains of intracellular L. pneumophila.
Insights
Clarithromycin, azithromycin, and erythromycin show potent antibacterial effects against Legionella pneumophila. All three macrolides effectively inhibited both extracellular and intracellular bacterial growth, demonstrating their therapeutic potential.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- Legionella pneumophila is a significant cause of bacterial pneumonia.
- Macrolide antibiotics are a primary treatment for Legionnaires' disease.
- Understanding the comparative efficacy of different macrolides against L. pneumophila is crucial for effective treatment.
Purpose of the Study:
- To compare the in vitro antibacterial activity of clarithromycin, azithromycin, and erythromycin against Legionella pneumophila.
- To evaluate the efficacy of these macrolides against both extracellular and intracellular L. pneumophila.
Main Methods:
- Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs) were determined using microdilution assays.
- Antibacterial activity was assessed against five strains of L. pneumophila, including a reference strain and clinical isolates.
- Intracellular activity was tested using L. pneumophila grown within MRC-5 human lung fibroblast cells.
Main Results:
- Clarithromycin exhibited the highest extracellular activity (MIC < or = 0.015-0.06), followed by azithromycin (MIC 0.03-0.12) and erythromycin (MIC 0.06-0.25).
- At concentrations of 2x and 8x the extracellular MBC, all three macrolides demonstrated equal effectiveness in inhibiting intracellular L. pneumophila growth.
- All tested macrolides were effective against both extracellular and intracellular forms of L. pneumophila.
Conclusions:
- Clarithromycin, azithromycin, and erythromycin are effective against Legionella pneumophila.
- These macrolides show comparable efficacy in inhibiting intracellular L. pneumophila, suggesting broad clinical utility.
- The study supports the use of these macrolides in treating Legionnaires' disease.