Subcellular Quantification of Uptake in Gram-Negative Bacteria

Area of Science:

• Microbiology
• Pharmacology
• Biochemistry

Background:

• Gram-negative bacterial infections pose a significant healthcare challenge due to a scarcity of new antibiotics.
• Limited understanding of how small molecules enter and exit Gram-negative bacteria hinders antibiotic development.

Purpose of the Study:

• To develop a versatile, label-free assay for determining intracellular localization and concentration of compounds in Gram-negative bacteria.
• To provide crucial data for the rational optimization of novel antibiotics against Gram-negative pathogens.

Main Methods:

• A fractionation procedure was used to isolate periplasm, cytoplasm, and membrane components from treated Escherichia coli cells.
• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantified antibiotic content in each bacterial compartment.
• Bacterial cell geometry was used to convert antibiotic amounts to compartment-specific concentrations.

Main Results:

• The assay successfully quantified diverse antibiotics (ciprofloxacin, tetracycline, trimethoprim, erythromycin) across different bacterial compartments.
• Significant variations in uptake and distribution patterns were observed among the tested antibiotics.
• Ciprofloxacin showed higher concentration in the periplasm compared to the cytoplasm, despite lower absolute amounts.
• Uptake differences for erythromycin and tetracycline did not directly correlate with observed Minimum Inhibitory Concentrations (MICs) between wild-type and efflux-impaired strains.

Conclusions:

• The developed assay provides essential compartment-specific antibiotic concentration data for Gram-negative bacteria.
• This information is critical for improving the rational design and optimization of new antibacterial agents.
• Further research is needed to fully correlate uptake data with antibiotic efficacy predictions.