QUANTIFICATION, QUALIFICATION, AND MICROBIAL KILLING EFFICIENCIES OF ANTIMICROBIAL CHLORINE-BASED SUBSTANCES PRODUCED BY IONTOPHORESIS

The dependence of microbial killing on chloride ions present in soluti ons undergoing iontophoresis is addressed. A 400-mu A current was appl ied to vials containing synthetic urine or saline, and the production of chlorine-based substances (CBSs) was detected by the N,N-diethyl-p- phenylene diamine colorimetric method. It was found that as the time o f current application increased, the total concentration of CBSs also increased. The iontophoretic current converted (through oxidation) chl oride ions present in the solutions into CBSs such as free chlorine, c hlorine dioxide, chlorite, monochloramine, and dichloramine (the last two were produced by iontophoresis only when nitrogenous substances we re present in the solution). Two of the CBSs (free Cl and ClO2), when they were separately added back to microbial suspensions (approximatel y 3 x 10(5) CFU/ml) at the same concentrations at which they were dete cted in either 0.46% (wt/vol) NaCl solution or synthetic urine iontoph oresed for 4 h at 400 mu A, reduced or eliminated bacterial genera and a fungus. However, when free Cl and ClO2 were jointly added back to m icrobial suspensions, bacterial and fungal killing was synergistic and more rapid and complete than when these chlorine-based biocides were added separately. Therefore, iontophoresis of solutions containing chl oride ions produces chlorine-based biocides that are responsible for t he antimicrobial effect of iontophoresis.