Gold-Decorated M13 I-Forms and S-Forms for Targeted Photothermal Lysis of Bacteria

With the emergence of multidrug-resistant bacteria, photothermal therapy has been proposed as an alternative to antibiotics for targeting and killing pathogens. In this study, two M13 bacteriophage polymorphs were studied as nanoscaffolds for plasmonic bactericidal agents. Receptor-binding proteins found on the pIII minor coat protein targeted Escherichia coli bacteria with F-pili (F⁺ strain), while a gold-binding peptide motif displayed on the pVIII major coat protein templated Au nanoparticles. Temperature-dependent exposure to a chloroform-water interface transformed the native filamentous phage into either rod-like or spheroid structures. The morphology, geometry, and size of the polymorphs, as well as the receptor-binding protein and host cell receptor interaction were studied using electron microscopy. Au/template structures were formed through incubation with Au colloid, and optical absorbance was measured. Despite the closely packed Au nanoparticle layer on the surface the viral scaffolds, electron microscopy confirmed that host receptor affinity was retained. Photothermal bactericidal studies were performed using 532 nm laser irradiation with a variety of powers and exposure times. Bacterial viability was assessed using colony count. With the shape-modified M13 scaffolds, up to 64% of E. coli were killed within 20 min. These studies demonstrate the promise of i-form and s-form polymorphs for the directed plasmonic-based photothermal killing of bacteria.