A New Method for the Detection and Enumeration of Xylitol-resistant (fructose-PTS⁻) Strains ofStreptococcus mutansfrom Pure Cultures and Human Saliva

Abstract

A simple procedure for the identification and enumeration, in large bacterial populations, of Streptococcus mutans of both xylitol-resistant and xylitol-sensitive phenotypes was developed. Since xylitol-resistant cells have lost the capacity to take up xylitol from the extracellular medium, due to a defect in their fructose-PTS, there is no uptake of [14C]xylitol by these cells whereas the [14C]xylitol taken up by the sensitive cells is used to visualise them by autoradiography. The method was shown to be suitable for laboratory strains as well as for natural populations of S. mutans ofthe human oral cavity. The in vitro selection of the xylitol-resistant phenotype during consecutive periods of growth at the expense of glucose in the presence of xylitol was followed. Likewise, it was found that the average percentage of xylitol-resistant fresh isolates from two human subjects increased from 0 per cent to 78 per cent over a xylitol-consuming period of 17 d, while it increased from 0 per cent to 8 per cent only in the control subjects who were consuming sorbitol and mannitol instead of xylitol. The superiority of this method resides in the possibility of processing many samples simultaneously. Moreover, it can be applied successfully to the detection and enumeration of other types of PTS mutants if the radioactive xylitol is replaced with a sugar analogue of the defective PTS. A strain of S. salivarius, defective in mannose-PTS, was identified with 2-deo~y-['~C]glucose.

Cariogenic traits in xylitol‐resistant and xylitol‐sensitive mutans streptococci

“…On the contrary, natural selection and emergence of mutans streptococci that are resistant to xylitol seem to take place (25, 27). Several studies have shown that emergence of X‐R mutans streptococci occurs rapidly (8), and that the ratio X‐R/X‐S is increased in habitual xylitol consumers (27). Xylitol has no growth‐inhibiting effect on X‐R strains, as also confirmed in the present study.…”

Sucrose substitutes and their role in caries prevention

“…Possibly, the modest reduction in mutans streptococci is due to the 'fasting' effect of xylitol on oral microorganisms. The adaptation of S.mutans to xylitol has been recognised [73][74][75][76][77] , although the effect of xylitol-insensitive strains of S.mutans on fermentable carbohydrates and on glucan synthesis from sucrose has not been clarified.…”

Effect of xylitol on mutans streptococci and lactic acid formation in saliva and plaque from adolescents and young adults with fixed orthodontic appliances

“…The autoradiography method described by D réan & T rahan (20) formed the base for this analysis. A sterile cellulose nitrate filter (0.45 µm; Sartorius, Bie & Berntsen, Rødovre, Denmark) was placed on a modified MSB agar containing 30% sucrose.…”