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The inhibition of streptococci by lactoperoxidase, thiocyanate and hydrogen peroxide. The oxidation of thiocyanate and the nature of the inhibitory compound.

ABSTRACT: 1. The products of the lactoperoxidase-catalysed oxidation of thiocyanate by hydrogen peroxide were sulphate, carbon dioxide and ammonia. Cyanate, sulphite and a compound showing increased extinction at 235mmu (the ;235 compound') were intermediate oxidation products. 2. Two of the intermediates acted as electron acceptors in the oxidation of NADH(2). Thus NADH(2) was oxidized by sulphite in the presence of lactoperoxidase (EC 1.11.1.7) and Mn(2+) and by the ;235 compound' in the presence of an enzyme, the NADH(2)-oxidizing enzyme, present in extracts of lactoperoxidase-resistant streptococci. Sulphur dicyanide also acted as an electron acceptor in the latter reaction. The ;235 compound' was also reduced non-enzymically by sulphite. 3. The glycolysis of lactoperoxidasesensitive streptococci suspended in glucose solution was not inhibited by sulphite, cyanate, cyanide or the ;235 compound' but was inhibited by sulphur dicyanide. The inhibition by 0.1mm-sulphur dicyanide could be reversed, as could that caused by lactoperoxidase, thiocyanate and hydrogen peroxide, by washing the cells or by the addition of a cell-free extract of a lactoperoxidase-resistant streptococcus. 4. The effects of 0.1mm-sulphur dicyanide on catabolic enzymes of resting streptococci were very similar to those of the lactoperoxidase-thiocyanate-hydrogen peroxide system. Thus hexokinase was completedly inhibited, glucose 6-phosphate dehydrogenase and aldolase were partially inhibited and phosphohexokinase was little affected in both cases.

SUBMITTER: Oram JD

PROVIDER: S-EPMC1265146 | biostudies-other | 1966 Aug

REPOSITORIES: biostudies-other

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Project description:Commensal Streptococcus sanguinis and Streptococcus gordonii are pioneer oral biofilm colonizers. Characteristic for both is the SpxB-dependent production of H2O2, which is crucial for inhibiting competing biofilm members, especially the cariogenic species Streptococcus mutans H2O2 production is strongly affected by environmental conditions, but few mechanisms are known. Dental plaque pH is one of the key parameters dictating dental plaque ecology and ultimately oral health status. Therefore, the objective of the current study was to characterize the effects of environmental pH on H2O2 production by S. sanguinis and S. gordoniiS. sanguinis H2O2 production was not found to be affected by moderate changes in environmental pH, whereas S. gordonii H2O2 production declined markedly in response to lower pH. Further investigation into the pyruvate node, the central metabolic switch modulating H2O2 or lactic acid production, revealed increased lactic acid levels for S. gordonii at pH 6. The bias for lactic acid production at pH 6 resulted in concomitant improvement in the survival of S. gordonii at low pH and seems to constitute part of the acid tolerance response of S. gordonii Differential responses to pH similarly affect other oral streptococcal species, suggesting that the observed results are part of a larger phenomenon linking environmental pH, central metabolism, and the capacity to produce antagonistic amounts of H2O2IMPORTANCE Oral biofilms are subject to frequent and dramatic changes in pH. S. sanguinis and S. gordonii can compete with caries- and periodontitis-associated pathogens by generating H2O2 Therefore, it is crucial to understand how S. sanguinis and S. gordonii adapt to low pH and maintain their competitiveness under acid stress. The present study provides evidence that certain oral bacteria respond to environmental pH changes by tuning their metabolic output in favor of lactic acid production, to increase their acid survival, while others maintain their H2O2 production at a constant level. The differential control of H2O2 production provides important insights into the role of environmental conditions for growth competition of the oral flora.

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The inhibition of streptococci by lactoperoxidase, thiocyanate and hydrogen peroxide. The oxidation of thiocyanate and the nature of the inhibitory compound.

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