PCPDTBT Conjugated Polymer Nanoparticles for Photothermal Inactivation of Multidrug-Resistant <i>mcr-1</i>-Positive <i>Escherichia coli</i>

Antimicrobial resistance (AMR) poses a global health challenge, threatening the effectiveness of the current treatment of bacterial infections. The emergence of plasmid-mediated resistance, notably the <i>mcr-1</i> gene in <i>Escherichia coli</i> (<i>E. coli</i>), further complicates therapeutic options by conferring resistance to colistin, a last-resort antibiotic. This study explores the potential of conjugated polymer nanoparticles made of poly-[2,6-(4,4-bis-(2-ethylhexyl)-4<i>H</i>-cyclopenta-[2,1-<i>b</i>;3,4-<i>b</i>']-dithiophene)-<i>alt</i>-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT NPs) for antimicrobial photothermal therapy (PPT) against multidrug-resistant, <i>mcr-1</i>-positive <i>E. coli</i> strains. PCPDTBT NPs were synthesized through nanoprecipitation and characterized for their photothermal response upon near-infrared (NIR) laser irradiation at 806 nm (1.13 W). The nanoparticles exhibited efficient absorption in the NIR range and generated substantial photothermal heating sufficient for bacterial inactivation. PCPDTBT NPs maintained their photothermal performance without degradation across multiple irradiation cycles. Photoinactivation assays confirmed PCPDTBT NPs' (17 mg L^-1) ability to significantly reduce bacterial viability, particularly against <i>mcr-1-</i>positive <i>E. coli</i>. Scanning electron microscopy (SEM) images confirmed pronounced damage to bacterial cells following photothermal treatment. Overall, PCPDTBT NPs are highly promising as standalone agents for PPT against antibiotic-resistant pathogens, indicating their potential for future therapeutic strategies.