Repurposing of Near-Infrared IR 808: A Promising Agent for the Treatment of Gram-Positive Bacteria Induced Endophthalmitis

Bacterial endophthalmitis is commonly treated with intravitreal antibiotic injections. However, the extensive use of antibiotics can readily exacerbate bacterial resistance, highlighting the urgent need for alternative antibacterial strategies. Herein, we synthesized a near-infrared heptamethine cyanine small molecule, IR 808, and explored its feasibility as an antibacterial agent for the treatment of bacterial endophthalmitis. Results demonstrated that IR 808 exhibited superior photodynamic properties, which synergistically enhanced its antibacterial efficacy. Specifically, IR 808 at a low concentration of 2 μM, when irradiated with an 808 nm laser (0.8 W/cm², 10 min) achieved over 99% antibacterial efficacy against <i>Staphylococcus aureus</i> (<i>S. aureus</i>) and <i>Staphylococcus epidermidis</i> (<i>S. epidermidis</i>), significantly outperforming the clinically used indocyanine green (ICG). In a rat model of endophthalmitis induced by <i>S. aureus</i>, IR 808 combined with 808 nm laser irradiation effectively killed bacteria, suppressed intraocular inflammatory responses, and mitigated retinal structural damage. Additionally, IR 808 was confirmed to have satisfactory cellular and tissue compatibility at effective antibacterial doses in both <i>in vitro</i> and <i>in vivo</i> experiments. Therefore, IR 808 holds promise as a viable agent for the antibacterial treatment of bacterial endophthalmitis caused by Gram-positive bacteria.