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Comparative in vitro activity, serum binding and binding activity interactions of the macrolides A-56268, RU-28965,
G A Dette1, H Knothe, G Koulen
1Department of Medical Microbiology, J.W. Goethe University, Frankfurt, Federal Republic of Germany.
Abstract:
The minimal inhibitory concentrations of macrolide antibiotics against staphylococci, streptococci and Haemophilus influenzae were determined in vitro. A-56268 was the most active and RU-28965 was the least active of the macrolides tested. The interaction at erythromycin binding sites in serum and at alpha 1-acid glycoprotein was studied. RU-28965 exhibited the highest binding affinity. The effect of binding on antimicrobial potencies was evaluated by measurements of the first-order generation rate constants and by determination of MICs of staphylococci in broth and in human serum. The activity of each of the macrolides was lowered by serum binding, but only that of RU-28965 was dramatically decreased.
Insights
New macrolide antibiotics were tested against common bacteria. While A-56268 showed high activity, RU-28965 was less potent, especially when bound to serum proteins, significantly reducing its effectiveness.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- Macrolide antibiotics are crucial for treating bacterial infections.
- Understanding macrolide-antibiotic interactions with biological molecules like serum proteins is vital for predicting in vivo efficacy.
- Variations in antibiotic potency against common pathogens like Staphylococcus, Streptococcus, and Haemophilus influenzae necessitate the development of new agents.
Purpose of the Study:
- To determine the in vitro activity of novel macrolide antibiotics against key bacterial pathogens.
- To investigate the binding interactions of macrolides with serum components, specifically alpha-1-acid glycoprotein.
- To evaluate how serum binding affects the antimicrobial potency of macrolides.
Main Methods:
- Determination of minimal inhibitory concentrations (MICs) for macrolides against Staphylococcus, Streptococcus, and Haemophilus influenzae.
- In vitro binding studies to assess interactions with erythromycin binding sites and alpha-1-acid glycoprotein.
- Measurement of first-order generation rate constants and MICs in broth versus human serum to quantify the impact of protein binding.
Main Results:
- A-56268 demonstrated the highest in vitro activity, while RU-28965 was the least active among the tested macrolides.
- RU-28965 exhibited the strongest binding affinity to serum components and alpha-1-acid glycoprotein.
- Serum binding significantly reduced the antimicrobial activity of all tested macrolides, with a particularly dramatic decrease observed for RU-28965.
Conclusions:
- Macrolide antibiotic activity against staphylococci, streptococci, and H. influenzae varies significantly.
- High binding affinity to serum proteins, as seen with RU-28965, can substantially diminish antimicrobial efficacy in a clinical setting.
- Further research into macrolide-serum protein interactions is essential for optimizing antibiotic therapy and drug development.