Growth Phase Contribution in Dictating Drug Transport and Subcellular Accumulation inside Escherichia coli

Area of Science:

• Microbiology
• Biophysics

Background:

• Bacteria exhibit distinct growth phases influencing cellular properties.
• Gram-negative bacteria possess a complex dual-membrane envelope complicating drug permeation studies.
• Drug efficacy often decreases in nongrowing bacterial phases, potentially leading to multidrug resistance.

Purpose of the Study:

• To investigate changes within the bacterial envelope during different growth phases.
• To quantify drug permeation and accumulation across bacterial membranes and compartments during growth.
• To understand the impact of bacterial life cycle on drug transport kinetics.

Main Methods:

• Utilized nonlinear optical technique, second-harmonic generation (SHG) spectroscopy.
• Probed transport kinetics and accumulation of quaternary ammonium compounds (QACs) like malachite green in *Escherichia coli*.
• Employed fluorescence microscopy to study another QAC, propidium iodide.

Main Results:

• Actively growing cells demonstrated significantly faster drug transport and higher cytoplasmic accumulation compared to slow or nongrowing cells.
• The *rpoS* gene was identified as critical in regulating drug transport during the saturation growth phase.
• Bacterial membrane permeability exhibited gradual alterations preceding the onset of subsequent growth phases.

Conclusions:

• Bacterial growth phase is a critical determinant of drug transport and accumulation.
• Understanding growth-phase-dependent changes in membrane permeability is essential for predicting drug efficacy.
• Reporting bacterial growth rate and phase is crucial for accurate drug efficacy assessments.