Infection Research Group, Dental Institute, King's College London, London, United Kingdom.
PLoS One. 2010 Feb 5;5(2):e9073. doi: 10.1371/journal.pone.0009073.
Streptococcus mutans, consisting of serotypes c, e, f and k, is an oral aciduric organism associated with the initiation and progression of dental caries. A total of 135 independent Streptococcus mutans strains from caries-free and caries-active subjects isolated from various geographical locations were examined in two versions of an MLST scheme consisting of either 6 housekeeping genes [accC (acetyl-CoA carboxylase biotin carboxylase subunit), gki (glucokinase), lepA (GTP-binding protein), recP (transketolase), sodA (superoxide dismutase), and tyrS (tyrosyl-tRNA synthetase)] or the housekeeping genes supplemented with 2 extracellular putative virulence genes [gtfB (glucosyltransferase B) and spaP (surface protein antigen I/II)] to increase sequence type diversity. The number of alleles found varied between 20 (lepA) and 37 (spaP). Overall, 121 sequence types (STs) were defined using the housekeeping genes alone and 122 with all genes. However pi, nucleotide diversity per site, was low for all loci being in the range 0.019-0.007. The virulence genes exhibited the greatest nucleotide diversity and the recombination/mutation ratio was 0.67 [95% confidence interval 0.3-1.15] compared to 8.3 [95% confidence interval 5.0-14.5] for the 6 concatenated housekeeping genes alone. The ML trees generated for individual MLST loci were significantly incongruent and not significantly different from random trees. Analysis using ClonalFrame indicated that the majority of isolates were singletons and no evidence for a clonal structure or evidence to support serotype c strains as the ancestral S. mutans strain was apparent. There was also no evidence of a geographical distribution of individual isolates or that particular isolate clusters were associated with caries. The overall low sequence diversity suggests that S. mutans is a newly emerged species which has not accumulated large numbers of mutations but those that have occurred have been shuffled as a consequence of intra-species recombination generating genotypes which can be readily distinguished by sequence analysis.
变形链球菌由血清型 c、e、f 和 k 组成，是一种口腔产酸菌，与龋齿的发生和发展有关。从不同地理位置分离的无龋和有龋患者的 135 株独立变形链球菌菌株，分别用两种 MLST 方案进行了检测，这两种方案由 6 种管家基因[accC（乙酰辅酶 A 羧化酶生物素羧化酶亚基）、gki（葡萄糖激酶）、lepA（GTP 结合蛋白）、recP（转酮醇酶）、sodA（超氧化物歧化酶）和 tyrS（酪氨酸-tRNA 合成酶）]或管家基因加上 2 种细胞外假定毒力基因[gtfB（葡聚糖转移酶 B）和 spaP（表面蛋白抗原 I/II）]组成，以增加序列型多样性。发现的等位基因数量在 20（lepA）和 37（spaP）之间变化。仅使用管家基因定义了 121 个序列型（ST），而使用所有基因则定义了 122 个序列型。然而，所有基因座的核苷酸多样性（pi）均较低，范围为 0.019-0.007。毒力基因显示出最大的核苷酸多样性，重组/突变比为 0.67[95%置信区间 0.3-1.15]，而仅 6 个串联管家基因的重组/突变比为 8.3[95%置信区间 5.0-14.5]。单独的 MLST 基因座生成的 ML 树明显不一致，与随机树无显著差异。使用 ClonalFrame 进行的分析表明，大多数分离株是单倍型，没有证据表明存在克隆结构或支持血清型 c 菌株是原始变形链球菌菌株的证据。也没有证据表明单个分离株的地理分布或特定的分离株群与龋齿有关。总的来说，低序列多样性表明变形链球菌是一种新出现的物种，尚未积累大量突变，但由于种内重组产生了可以通过序列分析容易区分的基因型，因此发生的突变已经被打乱。
