Photoinactivation of bacteria by hypocrellin-grafted bacterial cellulose
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With the aim of developing self-disinfecting materials to prevent pathogen transmission from surfaces to new hosts, here we report a simple and eco-friendly way to prepare photodynamic bacterial cellulose (BC) onto which the naturally-occurring photosensitizer hypocrellin (Hc) has been covalently appended. The resultant hypocrellin-grafted BC membrane (Hc-BC) was characterized by both physical (SEM, TGA, XRD) and spectroscopic (IR, diffuse reflectance UV–visible) methods, and the photosensitizer loading was found to be 155 nmol Hc/mg membrane. Indirect cytotoxicity tests employing mouse skin fibroblast (L929) cells showed no changes in cell viability, demonstrating that the Hc-BC membrane lacked any leachable components (e.g., unreacted coupling agent or hypocrellin) that could be cytotoxic to mammalian cells. The photodynamic antibacterial activity of Hc-BC was evaluated against gram-positive S. aureus (ATCC-6538) and gram-negative E. coli strain 8099. Our results demonstrated a 99.5 + % (2.7 log units) reduction in S. aureus upon illumination (Xe lamp, 65 ± 5 mW/cm2, 420–780 nm; 30 min), however, no statistically significant inactivation of E. coli was observed. Potentiation with potassium iodide was found to increase the antibacterial efficacy of Hc-BC against S. aureus to 99.997% (4.8 log units) at 10 mM KI, while E. coli was inactivated by 99.1% (2 log units) at 100 mM KI, with the increase in inactivation being attributable to short-lived reactive iodide radicals that are the major biocidal agents in the potentiation of Hc-BC by KI. Taken together, our findings demonstrated that hypocrellin-grafted bacterial cellulose is a sustainable material from which potent photodynamic antibacterial materials may be derived.
KeywordsAntibacterial photodynamic inactivation Bacterial cellulose Escherichia coli Hypocrellin Potassium iodide Staphylococcus aureus
We thank the financial support from the National Natural Science Foundation of China (No. 51603090), China Postdoctoral Science Foundation (No. 2018M630516), Provincial Policy Guidance Program (International Scientific and Technological Cooperation) (No. BZ2018032), and the Fundamental Research Funds for the Central Universities (JUSRP51907A).
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interest.
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