# Oxidative Treatment for Reducing Persistent Populations of Escherichia coli Under Amoxicillin and Gentamicin Pressure

## TL;DR

This study shows that combining light-based treatment with antibiotics can kill persistent bacteria more effectively and faster.

## Contribution

The study introduces optimized PDI with methylene blue to enhance antibiotic efficacy against persistent E. coli.

## Key findings

- PDI reduced MDK99 from >3 to 2 hours under amoxicillin pressure.
- PDI suppressed regrowth and reduced MDK99.99 from 3 to 2 hours under gentamicin pressure.
- SEM confirmed morphological damage consistent with bacterial persistence.

## Abstract

Bacterial persistence is a transient phenotypic state in which a subpopulation of cells survives antibiotic exposure without genetic resistance. These dormant, low‐metabolic cells are linked to recurrent infections and reduced antibiotic efficacy. Photodynamic inactivation (PDI), which generates reactive oxygen species (ROS) through photosensitizer activation under visible light, is a promising strategy to counteract persistence. This study evaluated PDI effects on Escherichia coli under amoxicillin and gentamicin pressure, using time‐kill assays and MDK99/MDK99.99 metrics. PDI, optimized with methylene blue (10 μM) and 10 J/cm2 light at 660 nm, was applied to antibiotic‐exposed cells and progeny. For amoxicillin, PDI reduced MDK99 from > 3 to 2 h; for gentamicin, it suppressed regrowth in progeny and reduced MDK99.99 from 3 to 2 h. Scanning electron microscopy showed morphological damage consistent with persistence. PDI enhanced antibiotic efficacy and shortened treatment time, supporting further investigation of PDI‐antibiotic combinations for chronic infections.

Photodynamic inactivation (PDI) with methylene blue and 660 nm LED enhances antibiotic killing of bacteria, accelerating time‐kill kinetics and reducing the MDK99 compared to antibiotics alone. SEM confirms effective cellular damage, demonstrating that PDI potentiates amoxicillin and gentamicin against tolerant bacterial populations.