Hydrogen peroxide excretion by oral streptococci and effect of lactoperoxidase-thiocyanate-hydrogen peroxide

Abstract

Approved type strains of Streptococcus sanguis, S. mitis, S. mutans, and S. salivarius were grown under aerobic and anaerobic conditions. The rate of hydrogen peroxide excretion, oxygen uptake, and acid production from glucose by washed-cell suspensions of these strains were studied, and the levels of enzymes in cell-free extracts which reduced oxygen, hydrogen peroxide, or hypothiocyanite (OSCN-) in the presence of NADH or NADPH were assayed. The effects of lactoperoxidase-thiocyanate-hydrogen peroxide on the rate of acid production and oxygen uptake by intact cells, the activity of glycolytic enzymes in cell-free extracts, and the levels of intracellular glycolytic intermediates were also studied. All strains consumed oxygen in the presence of glucose. S. sanguis, S. mitis, and anaerobically grown S. mutans excreted hydrogen peroxide. There was higher NADH oxidase and NADH peroxidase activity in aerobically grown cells than in anaerobically grown cells. NADPH oxidase activity was low in all species. Acid production, oxygen uptake, and, consequently, hydrogen peroxide excretion were inhibited in all the strains by lactoperoxidase-thiocyanate-hydrogen peroxide. S. sanguis and S. mitis had a higher capacity than S. mutans and S. salivarius to recover from this inhibition. Higher activity in the former strains of an NADH-OSCN oxidoreductase, which converted OSCN-into thiocyanate, explained this difference. The change in levels of intracellular glycolytic intermediates after inhibition of glycolysis by OSCNand the actual activity of glycolytic enzymes in cell-free extracts in the presence of OSCN-indicated that the primary target of OSCN-in the glycolytic pathway was glyceraldehyde 3-phosphate dehydrogenase.

Effects of delmopinol on antimicrobial peroxidase systems and lysozyme in vitro and in human whole saliva

“…It should be mentioned that delmopinol has usually been tested as a 0.2% mouthrinse, which is equivalent to 6.5 mM delmopinol. Even more interesting is the possible interference of delmopinol with the formation of hypothiocyanite (HOSCN/OSCN"), which is the actual peroxi-dase-generated antimicrobial agent in vivo (10,16,24). In the present study, delmopinol (6.5 mM) significantly reduced peroxidase-mediated HOSCN/ OSCN~ generation in whole saliva, in particular at low pH.…”

“…The acttial antimicrobial agent produced by both peroxidases is hypothiocyanite (HOSCN/OSCN"), formed by peroxidase-generated oxidation of thiocyanate (SCN~) in the pres-ence of HjOj (9). HOSCN/OSCN-is antimicrobial against a number of oral gram-positive (10,11) and gram-negative (12) bacteria, fungi (13) and viruses (14,15). It also inhibits glucose-stimulated acid production of dental plaque in a dose-dependent way (16).…”

“…Activity of human lysozyme(10,25, 50 and 100 mg/ml HLZ) in the presence of 6.5 mM deimopinol. HLZ-delmopinol mixture was incubated in 0.1 M phosphate buffer at pH 6.0 for 5 min before the assay.…”

Combined inhibitory effect of lactoferrin and lactoperoxidase system on the viability of Streptococcus mutans, serotype c

“…In contrast to that of apo LF, the baetericidal effect of HOSCN/OSCN" against S. mutans at low pH is a new observation. Studies of the inhibitory action of HOSCN/ OSCN" against S. mutans, serotype c, have so far indicated only bacteriostatic, antimetabolic activity against this microorganism (10,11,13,20,23). However, when myeloperoxidase was used instead of LP at low pH together with SCN" ions and H2O2 against S. mutans, bactericidal activity was also reported (24).…”

“…The antibacterial factors were used in concentrations normally found in human saliva or plaque fluid (1). S. mutans, serotype c, was chosen as a target microorganism because its response to both peroxidase systems (10)(11)(12)(13) and LF (9) as separate antibacterial agents is already well characterized. Furthermore, S. mutans serotype c strains are highly cariogenic (14) and their inhibition by the combined action of these two oral defense systems is interesting because both systems have been incorporated in some commercial oral health products, such as toothpastes and mouthsprays.…”