Quantitative Evaluation of Nucleic Acid Degradability of Copper Alloy Surfaces and Its Correlation to Antibacterial Activity.

Copper (Cu) and its alloys have bactericidal activity known as "contact killing" with degradation of nucleic acids inside the bacteria, which is beneficial to inhibit horizontal gene transfer (HGF). In order to understand the nucleic acid degradability of Cu and its alloy surfaces, we developed a new in vitro method to quantitatively evaluate it by a swab method under a "dry" condition and compared it with that of commercially available antibacterial materials such as antibacterial stainless steel, pure silver, and antibacterial resins. As a result, only Cu and its alloys showed continuous degradation of nucleic acids for up to 6 h of contact time. The nucleic acid degradability levels of the Cu alloys and other antibacterial materials correlate to their antibacterial activities evaluated by a film method referring to JIS Z 2801:2012 for Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. Nucleic acid degradation by copper (I) and (II) chlorides was confirmed at the ranges over 10 mM and 1-20 mM, respectively, suggesting that the copper ion release may be responsible for the degradation of the nucleic acids on Cu and its alloy surfaces. In conclusion, the higher Cu content in the alloys gave higher nucleic acid degradability and higher antibacterial activities.