Expulsion mechanism of xylitol 5‐phosphate in Streptococcus mutans

Abstract

– The expulsion mechanism of xylitol 5‐phosphate in Streptococcus mutans ATCC 25175 was studied using resting cells incubated in the presence of 14C‐xylitol. The expulsion appeared to be a two‐step process: xylitol 5‐phosphate was first hydrolyzed to xylitol and inorganic phosphate, and the xylitol was subsequently expelled from the cells. The dephosphorylation step appeared to be energy‐requiring and it was most likely associated with a phosphatase which was active on xylitol 5‐phosphate. Two to three successive cultivations of the cells in the presence of 6% xylitol increased this enzyme activity 4.3‐fold. These results are in accordance with the presence of an energy‐dependent xylitol 5‐phosphate cycle in S. mutans, which is regulated by exogenous xylitol.

Xylitol and caries prevention — is it a magic bullet?

“…[52][53][54] Xylitol can act in a bacteriostatic way: some strains of oral streptococci take up xylitol and convert it to xylitol-5-phosphate, resulting in the formation of intra-cellular vacuoles and degraded cell membranes. [55][56][57][58][59] Xylitol can cause a 'futile metabolic cycle' . Streptococcus strains take up xylitol and phosphorylate it to xylitol -5-phosphate.…”

“…This is then split by sugar-phosphate phosphatases and the xylitol is then expelled from the cell. [59][60][61][62] caries studies. Remineralisation occurred in nearly all experiments where non-sugar sweeteners were used during the 'healing' phase but there was no clear indication that xylitol had any greater effect than other non-sugar sweeteners when evaluated in short-term studies.…”

“…[52][53][54] Third, in-vitro studies have shown some strains of oral streptococci take up xylitol and convert it to xylitol-5-phosphate resulting in the development of intra-cellular vacuoles and degraded cell membranes in mutans and sobrinus streptococci, and through this mechanism xylitol is acting in a bacteriostatic way. [55][56][57][58][59] Lastly, some streptococcal strains take up xylitol which participates in what is termed 'the futile metabolic cycle' . [59][60][61][62] In this cycle, xylitol is taken into the cell, phosphorylated to xylitol-5-phosphate, and is then split by sugar-phosphate phosphatases and the resulting xylitol is expelled from the cell.…”

“…[55][56][57][58][59] Lastly, some streptococcal strains take up xylitol which participates in what is termed 'the futile metabolic cycle' . [59][60][61][62] In this cycle, xylitol is taken into the cell, phosphorylated to xylitol-5-phosphate, and is then split by sugar-phosphate phosphatases and the resulting xylitol is expelled from the cell. The clinical relevance of this process has not yet been established, but it is more likely to benefit oral health than damage it.…”

Metabolomic Effects of Xylitol and Fluoride on Plaque Biofilm in Vivo

“…Xylitol is known to repress acid production from glucose by S. mutans through the inhibition of glycolytic enzymes by xylitol 5-phosphate (X5P) produced from xylitol by a constitutive phosphoenolpyruvate:fructose phosphotransferase system (Assev and Rölla, 1984;Trahan et al, 1985;Trahan, 1995;Miyasawa et al, 2003). Further, X5P is dephosphorylated and returned to xylitol, resulting in the formation of a "futile cycle", an energy-wasting cycle, and the subsequent repression of growth of S. mutans (Pihlanto-Leppälä et al, 1990;Trahan et al, 1991). Although it is true that xylitol does not cause dental caries, the inhibitory mechanism of xylitol has not been confirmed in plaque biofilm in vivo.…”