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Uptake of indolmycin in gram-positive bacteria
Abstract:
The antimicrobial activity of indolmycin correlates with the generation time of the investigated strains. Thus, in Staphylococcus aureus ATCC 13150 with a 37-min generation time, the minimal inhibitory concentration (MIC) was 0.6 microgram ml-1, and in Bacillus subtilis ATCC 27142 with a generation time of 23 min, the MIC reached 10.5 micrograms ml-1. Competition experiments in staphylococci and B. subtilis with aromatic amino acids demonstrated that indolmycin uses the uptake systems that are responsible for tryptophan. When the Ki values of indolmycin for the uptake of the aromatic amino acids in staphylococci were compared, there was a significantly higher influence on the uptake of tryptophan with respect to phenylalanine and tyrosine. In addition, indolmycin low resistant mutants of S. aureus ATCC 13150 showed a 10- to 100-fold decrease in Km value for the uptake of tryptophan and a 10-fold decrease for tyrosine uptake. The Km value for phenylalanine remained unchanged. A significant correlation existed between the Ki values of indolmycin for the uptake of tryptophan in the wild-type strains of S. aureus and B. subtilis and the MIC against the corresponding strain. Low Ki values corresponded to low MIC. These results imply that, in addition to improvement of the antibiotic structure for target affinity, the tryptophan uptake system can be used as a test model for the structural evaluation of indolmycin with respect to an increased transport activity into bacterial cells.
Insights
Indolmycin
Area of Science:
- Microbiology
- Bacterial Physiology
- Drug Discovery
Background:
- Indolmycin is an antibiotic with demonstrated antimicrobial activity.
- The precise mechanism of indolmycin's action and its relationship with bacterial growth rates require further elucidation.
Purpose of the Study:
- To investigate the correlation between indolmycin's antimicrobial activity and bacterial generation time.
- To identify the specific nutrient uptake systems utilized by indolmycin.
- To evaluate the potential of the tryptophan uptake system as a model for assessing indolmycin's efficacy.
Main Methods:
- Minimal inhibitory concentration (MIC) determination for Staphylococcus aureus and Bacillus subtilis strains with varying generation times.
- Competition experiments using aromatic amino acids to probe indolmycin's interaction with nutrient uptake systems.
- Kinetic analysis (Ki and Km values) of indolmycin's effect on tryptophan, phenylalanine, and tyrosine uptake in wild-type and resistant bacterial strains.
Main Results:
- Antimicrobial activity of indolmycin positively correlates with bacterial generation time.
- Indolmycin specifically targets tryptophan uptake systems in S. aureus and B. subtilis.
- Mutant analysis revealed significant alterations in tryptophan and tyrosine uptake kinetics, but not phenylalanine uptake.
- A strong correlation was observed between indolmycin's inhibition constant (Ki) for tryptophan uptake and its minimal inhibitory concentration (MIC).
Conclusions:
- Indolmycin's efficacy is influenced by bacterial growth rate and its specific interaction with tryptophan uptake pathways.
- The tryptophan uptake system serves as a valuable model for evaluating and optimizing indolmycin's structure for enhanced bacterial cell transport and activity.
- These findings provide insights for developing novel antimicrobial strategies targeting essential amino acid transport systems.