Cationic Oligo(thiophene ethynylene) with Broad-Spectrum and High Antibacterial Efficiency under White Light and Specific Biocidal Activity against <i>S. aureus</i> in Dark

Abstract

We designed and synthesized a novel oligo­(thiophene ethynylene) (OTE) to investigate the antibacterial activities against Gram-positive (<i>Staphylococcus aureus</i> and <i>Staphylococcus epidermidis</i>) and Gram-negative (<i>Ralstonia solanacearum</i> and <i>Escherichia coli</i>) bacteria in vitro by photodynamic therapy (PDT). Notably, OTE presents broad-spectrum and greatly high antibacterial activities after white light irradiation at nanogram per milliliter concentrations. The half inhibitory concentrations (IC<sub>50</sub>) values obtained for <i>S. aureus</i>, <i>S. epidermidis</i>, <i>E. coli</i>, and <i>R. solanacearum</i> are 8, 13, 24, and 52 ng/mL after illumination for 30 min, respectively, which are lower than that of other PDT agents. Interestingly, OTE shows the specific and very strong dark killing capability against <i>S. aureus</i> at the concentration of 180 ng/mL for 30 min, which is the highest efficiency biocide against <i>S. aureus</i> without the need of irradiation to date. The antibacterial mechanism investigated demonstrated that reactive oxygen species or singlet-oxygen generated by OTE kills bacteria irreversibly upon white light irradiation, and OTE as a v-type oligomer exerts its toxicity directly on destroying bacterial cytoplasmic membrane in the dark. Importantly, the OTE shows no cell cytotoxicity and excellent biocompatibility. The results indicate that it is potential to provide versatile applications in the efficient control of pathogenic organisms and specific application for killing <i>S. aureus</i>

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