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Diffusion of aminoglycoside antibiotics across the outer membrane of Escherichia coli
Abstract:
The diffusion of aminoglycoside antibiotics (gentamicin, kanamycin, streptomycin, fradiomycin, lividomycin, and mannosylparomomycin) through porin pores was examined in vitro by the liposome swelling technique, using vesicle membranes reconstituted from phospholipids and purified porin trimers. Results showed that aminoglycoside antibiotics diffuse through porin-pores very efficiently, as rapidly as hexoses and disaccharides, despite the fact that the molecular weights of the aminoglycosides used were higher than or close to the exclusion limit of porin pores. The susceptibility to aminoglycoside antibiotics of mutant strains producing 3 to 4% of porin was not significantly different from that of a strain producing a wild-type quantity of porin. These results were interpreted to mean that aminoglycoside antibiotics diffuse through porin-pores very efficiently. Therefore, the diffusion of these drugs through the mutant outer membranes producing 3 to 4% of porin is not a rate-limiting step for aminoglycoside diffusion and its action.
Insights
Aminoglycoside antibiotics efficiently diffuse through bacterial porin pores, similar to sugars. This rapid diffusion means porin levels don't limit antibiotic action, even in low-porin mutants.
Area of Science:
- Microbiology
- Biochemistry
- Pharmacology
Background:
- Bacterial outer membranes act as selective barriers.
- Porins are essential protein channels in the outer membrane.
- Aminoglycoside antibiotics are crucial for treating bacterial infections.
Purpose of the Study:
- To investigate the diffusion efficiency of aminoglycoside antibiotics through porin pores.
- To determine if porin quantity affects aminoglycoside antibiotic susceptibility.
Main Methods:
- In vitro liposome swelling assay.
- Reconstitution of vesicle membranes with purified porin trimers.
- Examination of various aminoglycoside antibiotics (gentamicin, kanamycin, streptomycin, etc.).
Main Results:
- Aminoglycoside antibiotics diffused through porin pores as efficiently as hexoses and disaccharides.
- Diffusion remained efficient despite aminoglycoside molecular weights nearing the porin exclusion limit.
- Bacterial strains with reduced porin production (3-4% of wild-type) showed no significant difference in antibiotic susceptibility.
Conclusions:
- Aminoglycoside antibiotic diffusion through porin pores is highly efficient.
- The outer membrane's porin content is not a rate-limiting factor for aminoglycoside diffusion and efficacy.
- This implies porin channels readily facilitate the entry of these vital antibiotics.