Breaking bacterial tolerance and persistence with photodynamic inactivation

Tolerance and persistence phenotypes critically drive chronic infections and therapeutic failure. Such failure facilitates resistance-conferring mutations, exacerbating global bacterial resistance. This necessitates studies on combinatorial strategies to curb resistance escalation and address recurrent infection management. Gentamicin’s Minimum Inhibitory Concentration (MIC) was determined via standard protocols. Time-kill assays were conducted at MIC and post-photodynamic inactivation (PDI) using methylene blue as a 660 nm-activated photosensitizer. Gentamicin caused an exponential bacterial reduction on Day 1 (achieving MDK99 and a 3-log reduction), though persistent cells survived. Day 2 revealed heteroresistance, with unexpected post-1-hour growth. PDI pretreatment accelerated bacterial death (MDK99.99%) and induced a persistence-characteristic biphasic death curve in untreated progeny. Findings demonstrate that PDI pretreatment prior to antibiotics significantly altered mortality kinetics in bacterial cells and progeny.