Reaction Product Variability and Biological Activity of the Lactoperoxidase System Depending on Medium Ionic Strength and pH, and on Substrate Relative Concentration.

The potential of ions produced in water by the lactoperoxidase system against plant pests has shown promising results. We tested the bioactivity of ions produced by the lactoperoxidase oxidation of I- and SCN- in several buffers or in tap water and characterized the ions produced. In vitro biological activity was tested against Penicillium expansum, the causal agent of mold in fruits, and the major cause of patulin contamination of fruit juices and compotes. In buffers, the ionic concentration was increased 3-fold, and pathogen inhibition was obtained down to the 1:15 dilution. In tap water, the ionic concentration was weaker, and pathogen inhibition was obtained only down to the 1:3 dilution. Acidic buffer increased ion concentrations as compared to less acidic (pH 5.6 or 6.2) or neutral buffers, as do increased ionic strength. 13 C-labelled SCN- and MS showed that different ions were produced in water and in buffers. In specific conditions the ion solution turned yellow and a product was formed, probably diiodothiocyanate (I2 SCN- ), giving an intense signal at 49.7 ppm in 13 C-NMR. The formation of the signal was unambiguously favored in acidic media and disadvantaged or inhibited in neutral or basic conditions. It was enhanced at a specific SCN- : I- ratio of 1:4.5, but decreased when the ratio was 1:2, and was inhibited at ratio SCN- >I- . We demonstrated that the formation of the signal required the interaction between I2 and SCN- , and MS showed the presence of I2 SCN- .

Ex vivo decontamination of yeast-colonized dentures by iodine-thiocyanate complexes.

INTRODUCTION: Under well-defined experimental conditions, and in the presence of hydrogen peroxide, lactoperoxidase produces stable iodine-thiocyanate complexes that have antimicrobial properties. A novel process was developed to short circuit the consumption of hydrogen peroxide by microbial catalases by producing iodine-thiocyanate complexes prior to contact with microorganisms, with the aim of being able to decontaminate the ex vivo dentures colonized by yeasts. MATERIALS AND METHODS: Teabags containing lactoperoxidase adsorbed on inert clay beads were immersed for 1 minute in phosphate buffer solution (0.1 M pH 7.4) containing 5.2 mM potassium iodide, 1.2 mM potassium thiocyanate, and 5.5 mM hydrogen peroxide. After removing the adsorbed lactoperoxidase, the stability and efficacy of iodine-thiocyanate complexes for Candida-colonized denture decontamination were verified. Investigations were performed in vitro on Candida albicans ATCC 10231 and on clinical isolates from 46 dentures. A Candida plate count was performed after a 24-hour incubation at 37°C on Sabouraud-chloramphenicol or CHROMagar solid media; then, the yeast growth was evaluated in Sabouraud broth by turbidimetry and biofilm biomass by crystal violet staining. RESULTS: In vitro tests demonstrated the effectiveness of the oxidant solution in sterilizing a suspension of 106Candida cells per milliliter after a 5-minute incubation. A single ex vivo immersion of contaminated dentures in a solution of iodine-thiocyanate complexes led to a decrease of at least 1 log unit in the number of colony-forming units in 58.3% of the tested dentures, while immersing in water alone had no effect on denture colonization (significant c2: p = 0.0006). CONCLUSION: These data suggest a promising new strategy for decontamination of dentures.