Azithromycin-Induced Changes to Bacterial Membrane Properties Monitored in Vitro by Second-Harmonic Light Scattering

Area of Science:

• Microbiology
• Biophysics
• Pharmacology

Background:

• Bacterial membrane integrity is crucial for cell viability.
• Antimicrobial compounds can disrupt membrane function.
• Real-time monitoring of membrane changes is essential for understanding drug efficacy.

Purpose of the Study:

• To develop and apply a nonlinear light scattering method for real-time monitoring of antimicrobial-induced changes in bacterial membrane properties.
• To quantify the effect of azithromycin on the membrane permeability of *Escherichia coli*.

Main Methods:

• Utilized time-resolved second-harmonic light scattering (SHS) to monitor molecular adsorption and transport.
• Employed malachite green as a reporter molecule to assess membrane permeability.
• Studied living *Escherichia coli* in colloidal suspensions.

Main Results:

• Instantaneous azithromycin treatment did not significantly alter membrane permeability.
• One-hour pretreatment with sub-minimum inhibitory concentrations of azithromycin markedly increased outer and cytoplasmic membrane permeability.
• A new transport mechanism across the cytoplasmic membrane was facilitated by azithromycin pretreatment.

Conclusions:

• Second-harmonic light scattering (SHS) is a sensitive tool for detecting antimicrobial-induced alterations in bacterial membrane permeability.
• Sub-inhibitory azithromycin concentrations can significantly compromise bacterial membrane integrity.
• This method provides novel insights into antimicrobial action at the bacterial membrane level.