Infections resistant to existing antibiotics cause hundreds of thousands of deaths each year. According to some estimates, intrahospital infections caused by antibiotic-resistant bacteria are now ranked as the sixth leading cause of mortality in developed countries. Besides medicine, new antibiotics are also needed in other fields, such as agriculture and biotechnology. As a result, scientists are actively researching alternative antimicrobial materials capable of overcoming bacterial resistance. One of them is copper oxide nanoparticles (CuO), which demonstrate high activity against pathogenic microorganisms. It makes copper oxide nanoparticles commercially viable for use in paints, textiles, and antimicrobial coatings. Some studies suggest that such coatings can eliminate up to 99.9% of bacteria within two hours.
However, achieving such high efficiency in practice is challenging. The antimicrobial properties of this material strongly depend on various external factors. As part of a Russian Science Foundation project (Grant No. 24-16-20039), researchers at Tambov State University have demonstrated the crucial role of the chemical environment surrounding copper oxide nanoparticles in their antibacterial activity. The findings were published in the Nanomaterials journal.
"Unlike Gram-positive bacteria, Gram-negative bacteria have a thick cell membrane, making them more resistant to chemical damage and harder to combat. Therefore, we selected Gram-negative E. coli and simulated various realistic conditions under which copper oxide nanoparticles could act upon it. We tested different liquid media and various colloidal stabilizers. Besides, we used three different nanoparticle forms — flakes, rods and spheres,” explained Olga Zakharova, the Director of the Ecology and Biotechnology Research Center at Derzhavin State University and the lead author of the study.
The study revealed that the primary factor determining antibacterial effectiveness was not the size or shape of the nanoparticles but rather the chemical composition of their surrounding environment. In distilled water, all nanoparticle types exhibited the strongest antibacterial effects. The use of sodium dodecyl sulfate as a colloidal stabilizer significantly enhanced the toxicity of copper oxide nanoparticles, especially when combined with LB broth medium. It is interesting that the same stabilizer in an aqueous medium reduced the nanoparticles' antibacterial effect. In contrast, another stabilizer, Triton X-100, as well as saline solution, did not contribute to the nanoparticles' antibacterial action. Moreover, in some cases, bacterial growth was even observed.
According to the scientists, these findings could be applied in developing bactericidal and fungicidal drugs and coatings for medicine, agriculture, food technology, and biotechnology based on copper oxide nanoparticles. By carefully modeling the intended application environment, the antimicrobial potential of nanoparticles can be maximized. In the future, scientists plan to expand the range of studied pathogens and patent the most effective nanoparticle-chemical environment combinations as a new way to deal with them.
