Bacterial bioluminescence shows nanotexturing does not enhance antibacterial efficacy of zinc oxide membrane coatings

Abstract

Antibacterial membranes are often proposed for applications in which the membranes are in contact with the human body or in contact with food or drink, and hence their designs must minimize unintended toxicity. Zinc oxide (ZnO) is a well-known antibacterial agent and is relatively nontoxic, making it a promising material for the design of antibacterial membranes. Needle-like ZnO nanomaterials are believed to be additionally capable of a cell puncturing mechanism when they are agitated in suspension with bacteria. It is unclear, however, whether the puncturing mechanism is effective when the needle-like nanomaterials are immobilized as surface coatings. In this study, we assessed the antibacterial performance of two types of ZnO coatings synthesized on nylon membranes. One ZnO coating possessed no distinct hierarchical structure whereas the second consisted of ZnO microflowers each comprised of numerous ZnO nanoneedles, collectively forming a nanoneedle topography on the membrane surface. For antibacterial assessment of these coatings, we used several conventional assays and a variation of a recently developed bacterial bioluminescence monitoring assay. The conventional assays evaluated the antibacterial effects of zinc released from the membranes. The bioluminescence monitoring assay uniquely captured antibacterial effects of cell–surface contact between bacteria and the ZnO nanoneedle topography such as the puncture mechanism in question in real time without disturbing ongoing cell–surface interactions throughout incubation. Bioluminescent Staphylococcus aureus and bioluminescent Pseudomonas aeruginosa exposed to the ZnO nanoneedle topography exhibited loss and recovery of bioluminescence comparable to bacteria that were exposed to the ZnO coating without nanoneedle topography. We conclude that the nanotextured topography therefore did not further enhance antibacterial performance of the ZnO-coated membranes. S. aureus and P. aeruginosa were able to survive, recover, and proliferate directly atop the nanotextured ZnO coating.