An electrolysis method is described for generating an aqueous solution of copper citrate that has bacteriocidal activity against methicillin resistant Staphylococcus aureus (MRSA) bacteria. Gram positive bacteria are known to be relatively more sensitive to the bacteriocidal activities of copper ions than are Gram negative bacteria. Situations exist in which a disinfectant that is relatively more toxic for Gram positive bacteria will be advantageous over a more broadly active disinfectant, such as that provided by most other disinfectants. In particular, a disinfectant that is relatively selective for Gram positive bacteria could help preserve various non-pathogenic Gram negative microbial populations. The residual Gram negative bacteria can potentially compete with, and thereby lessen the chances of the reintroduction of pathogenic Gram positive bacteria, such as MRSA, Streptococcus, Clostridium difficile and Listeria monocytogenes.