Effect of lactoperoxidase on the antimicrobial effectiveness of the thiocyanate hydrogen peroxide combination in a quantitative suspension test

The bactericidal and fungicidal effects of lactoperoxidase on Streptococcus mutans and sanguinis and Candida albicans were evaluated by using two test mixtures of a 2.0% (w/v; 0.34 M) thiocyanate and 0.4% (w/v; 0.12 M) hydrogen peroxide solution, one without and one with lactoperoxidase. Following the quantitative suspension tests (EN 1040 and EN 1275), the growth of surviving bacteria and fungi in a nutrient broth was measured. The reduction factor in the suspension test without lactoperoxidase enzyme was < 1 for all three tested organisms. Thus, the mixtures of 2.0% (w/v; 0.34 M) thiocyanate and 0.4% (w/v; 0.12 M) hydrogen peroxide had no in vitro antimicrobial effect on Streptococcus mutans and sanguinis or Candida albicans. However, the suspension test with lactoperoxidase showed a high bactericidal and fungicidal effectiveness in vitro.The tested thiocyanate and H2O2 mixtures showed no relevant antimicrobial effect. However, by adding lactoperoxidase enzyme, the mixtures became not only an effective bactericidal (Streptococcus mutans and sanguinis) but also a fungicidal (Candida albicans) agent.Maintaining daily oral hygiene is essential to prevent caries, gingivitis, and periodontitis [1-3]. To support mechanical plaque control, which is mostly insufficient [4-6], antiseptics are used in toothpastes and mouth rinses [7-10].However, the concentrations and frequency of use of antiseptics are limited to avoid side effects, such as discoloration of teeth and tongue, taste alterations, mutations [11,12], and, for microbiostatic active agents, the risk of developing resistance or cross-resistance against antibiotics [13]. Therefore, it would seem better to stimulate or support the innate host defence system, such as the oral peroxidase-thiocyanate-hydrogen peroxide system.Human saliva contains peroxidase enzymes and lysozyme, among other innate host defence systems. The complete peroxidase system in saliva comprises three components: the peroxidase enzymes (glycopro