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

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/MDK_99.99 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 MDK_99.99 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.