Trahan L, Bourgeau G, Breton R
Groupe de Recherche en Ecologie Buccale, Faculté de médecine dentaire, Université Laval, Québec, Canada.
J Dent Res. 1996 Nov;75(11):1892-900. doi: 10.1177/00220345960750111201.
The growth inhibition of mutans streptococci is one of the proposed mechanisms of action of xylitol, a caries-preventive natural carbohydrate sweetener. Xylitol is taken up and accumulated as non-metabolizable, toxic xylitol phosphate via a constitutive fructose PTS, and selects, during in vitro growth at the expense of glucose, for natural xylitol-resistant mutants that lack constitutive fructose PTS activity. Since long-term xylitol consumption leads to the emergence of xylitol-resistant mutans populations in humans in an oral environment containing sugars of dietary origin, we wanted to test the hypothesis that xylitol-resistant cells could be selected from mutans streptococci strains during in vitro growth on fructose, sucrose, or lactose. Three laboratory strains and three fresh mutans streptococcal isolates were repeatedly transferred in trypticase-yeast extract medium supplemented with glucose, fructose, sucrose, or lactose in the presence and absence of xylitol. Depending on the growth sugar, the presence of xylitol resulted in the selection of xylitol-resistant populations for several of the six strains tested, but not necessarily in the presence of all four sugars. All six strains rapidly became xylitol-resistant when grown on glucose in the presence of xylitol. All three fresh isolates became xylitol-resistant after 9 to 16 transfers in the presence of fructose or sucrose plus xylitol, while none of the laboratory strains became xylitol-resistant after 16 transfers in the presence of these sugars. The growth rates of 12 xylitol-resistant mutants in the presence of eight sugars suggested the existence of various types of xylitol-resistant mutants. The data partially explain the occurrence of xylitol-resistant mutans populations in long-term xylitol consumers and suggest a mechanism consistent with a selection process. Since various preliminary results suggest that xylitol-resistant natural mutants may be less virulent and less cariogenic than their parent strains, this selection process may alter, for the better, the mutans streptococci population of the plaque and play a role in the caries-preventive action of xylitol.
变形链球菌的生长抑制是木糖醇（一种预防龋齿的天然碳水化合物甜味剂）的一种作用机制。木糖醇通过组成型果糖磷酸转移酶系统（PTS）以不可代谢的有毒木糖醇磷酸形式被摄取和积累，并在以葡萄糖为代价的体外生长过程中，选择缺乏组成型果糖PTS活性的天然木糖醇抗性突变体。由于长期食用木糖醇会导致在含有膳食来源糖类的口腔环境中，人类体内出现木糖醇抗性变形链球菌群体，我们想要测试这样一个假设：在以果糖、蔗糖或乳糖为培养基的体外生长过程中，可以从变形链球菌菌株中筛选出木糖醇抗性细胞。在有和没有木糖醇存在的情况下，将三株实验室菌株和三株新鲜分离的变形链球菌在补充有葡萄糖、果糖、蔗糖或乳糖的胰蛋白酶 - 酵母提取物培养基中反复传代培养。根据生长糖类的不同，木糖醇的存在导致在所测试的六株菌株中的几株筛选出了木糖醇抗性群体，但并非在所有四种糖类存在时都会出现这种情况。当在木糖醇存在的情况下于葡萄糖上生长时，所有六株菌株都迅速获得了木糖醇抗性。在果糖或蔗糖加木糖醇存在的情况下，经过9至16次传代后，所有三株新鲜分离株都获得了木糖醇抗性，而在这些糖类存在的情况下，经过16次传代后，没有一株实验室菌株获得木糖醇抗性。12个木糖醇抗性突变体在八种糖类存在情况下的生长速率表明存在各种类型的木糖醇抗性突变体。这些数据部分解释了长期食用木糖醇的人群中出现木糖醇抗性变形链球菌群体的现象，并提出了一种与选择过程一致的机制。由于各种初步结果表明，木糖醇抗性天然突变体可能比其亲本菌株的毒性和致龋性更低，这种选择过程可能会改善菌斑中的变形链球菌群体，并在木糖醇的防龋作用中发挥作用。
