Study on the pathogenicity of halitosis-causing agents and development of new method for the treatment

βC-S裂解酶催化l -半胱氨酸的α，β-消除生成硫化氢，硫化氢是口腔异味的主要原因之一，对哺乳动物细胞具有高毒性。我们评估了六种口腔链球菌产生硫化氢的能力。其中，蛇耳草粗酶提取液容量最大。然而，氨基酸序列的比较分析没有发现s.a anginosus βC-S裂解酶的任何有意义的差异。S.anginosus纯化的βC-S裂解酶对l -半胱氨酸的降解能力也非常高，而对l -半胱氨酸的降解能力不显著。这些发现表明，S.anginosus产生硫化氢的能力极高是由于该生物的βC-S裂解酶的独特特性。从血管链球菌中克隆了一个编码半胱硫氨酸γ-合成酶的基因（cgs），并对其蛋白进行了纯化和鉴定。cgs基因和直接下游的lcd基因作为一个操纵子共转录。高效液相色谱分析结果表明，该植物不仅具有半胱硫氨酸γ-合成酶活性，还具有o -乙酰高丝氨酸巯基水解酶活性。这些结果表明，弓形虫具有利用转硫和直接巯基化途径合成同型半胱氨酸的能力。我们检测了小鼠天然牙菌斑诱导脓肿的能力，菌斑产生的感染位点的微生物特征，以及微生物分离物的抗吞噬特性。使用不同的斑块样本，大多数小鼠均可诱导脓肿形成。与引起脓肿的菌斑样本相比，脓液的微生物组成非常简单。大多数分离物属于血管球菌群，通常是斑块样本的一小部分。这些结果表明，弓形虫的致病性与其大量产生硫化氢的能力有关。

βC-S Lyase catalyzes the α,β-elimination of L-cysteine to hydrogen sulfide, which is one of the main causes of oral malodor and is highly toxic to mammalian cells. We evaluated the capacity of six species of oral streptococci to produce hydrogen sulfide. The crude enzyme extract from S.anginosus had the greatest capacity. However, comparative analysis of amino acid sequences did not detect any meaningful differences in the S.anginosus βC-S lyase. The capacity of S.anginosus purified βC-S lyase to degrade L-cysteine was also extremely high, while its capacity to degrade L-cystathionine was unremarkable. These findings suggest that the extremely high capacity of S.anginosus to produce hydrogen sulfide is due to the unique characteristic of βC-S lyase from that organism.A gene (cgs) encoding cystathionine γ-synthase was cloned from Streptococcus anginosus, and its protein was purified and characterized. The cgs gene and the immediately downstream lcd gene were shown to be cotranscribed as an operon. HPLC analyses showed that the S.anginosus Cgs not only has cystathionine γ-synthase activity, but also expresses O-acetylhomoserine sulfhydrylase activity. These results suggest that S.anginosus has the capacity to utilize both the transsulfuration and direct sulfhydrylation pathways for homocysteine biosynthesis.We examined the abscess-inducing ability of native dental plaque in mice, the microbial features of the infectious locus produced by the plaque, and the anti-phagocytic property of microbial isolates. Abscess formation was induced in most mice using different plaque samples. The microbial composition of pus was very simple compared to that of the plaque sample that had induced the abscess. The majority of the isolates belonged to the S.anginosus group, normally a minor component of plaque samples. These results suggest that the pathogenicity of S.anginosus is related to its ability to produce hydrogen sulfide at high level.