Factors Enhancing the Antibacterial Effect of Monovalent Copper Ions

This study continues the series of experiments that demonstrate the high antibacterial properties of monovalent copper ions (Cu⁺). While in previous study we examined different metals (copper and silver) and their metal states (mono- and divalent), showing that monovalent copper is best for controlling bacterial growth, the current study focuses on finding conditions which further enhance the antibacterial effect of monovalent copper. This approach may also shed light on mechanisms of Cu⁺ ions which still remain unknown. To this end, the influence of Cu⁺ ions on model gram-negative Escherichia coli bacteria at different pH levels with a variety of carbon sources and elevated temperatures was examined. It was found that in both aerobic and anaerobic conditions in a poor growth medium, Cu²⁺ ions barely suppress any growth of E. coli, whereas Cu⁺ ions even at very low concentrations dramatically deplete bacterial populations in a time scale of minutes at room temperature, and less than one minute at elevated temperatures. Acidic pH, unfavorable carbon sources, and elevated temperatures boost the antibacterial action of Cu⁺ ions. On the whole, the study confirms that monovalent copper ions are strongly superior to divalent copper ions in their antibacterial action across a wide range of tested conditions.