棒状杆菌是革兰氏阳性，有氧，非含量，杆状细菌，其与放线菌相关。它们不会形成孢子或分支，只要形成孢子菌或分支，但它们具有在正常生长中形成不规则形状，球杆形或V形布置的特征。他们在细胞分裂后接受捕捉运动，使它们成为类似于中国信件的特征布置。棒状杆菌属包括一种不同的细菌组，包括动物和植物病原体，以及嗜孢子。一些棒状细菌是人类正常植物群的一部分，在几乎每一个解剖部位都在寻找合适的利基。最着名和最广泛研究的物种是棒状杆菌白喉，疾病的因果因子白喉。

历史和背景

没有人类的细菌疾病已成功地研究白喉。透射的病因，致病机制和外毒素的结构、功能和作用的分子基础已经明确确立。因此，已发展出治疗和预防白喉的高效方法。白喉棒状杆菌的研究与医学微生物学、免疫学和分子生物学的发展密切相关。白喉和白喉毒素的研究对这些领域以及我们对宿主-细菌相互作用的理解做出了许多贡献。希波克拉底在公元前4世纪首次提供了白喉的临床描述。在古叙利亚和埃及也有这种疾病的参考文献。在17世纪，致命的白喉流行病席卷了欧洲;在西班牙被称为" El garatillo "(扼杀者)，在意大利和西西里岛被称为"食道疾病"。在18世纪，这种疾病传播到美洲殖民地，并在1735年达到流行病的程度。通常，整个家庭在几周内死于这种疾病。引起白喉的细菌最早是由克莱伯斯在1883年描述的，并由莱弗勒在1884年培育，他应用科赫假设，正确地确定白喉棒状杆菌是疾病的病原体。 In 1884, Loeffler concluded that C. diphtheriae produced a soluble toxin, and thereby provided the first description of a bacterial exotoxin. In 1888, Roux and Yersin demonstrated the presence of the toxin in the cell-free culture fluid of C. diphtheriae which, when injected into suitable lab animals, caused the systemic manifestation of diphtheria. Two years later, von Behring and Kitasato succeeded in immunizing guinea pigs with a heat-attenuated form of the toxin and demonstrated that the sera of immunized animals contained an antitoxin capable of protecting other susceptible animals against the disease. This modified toxin was suitable for immunizing animals to obtain antitoxin but was found to cause severe local reactions in humans and could not be used as a vaccine. In 1909, Theobald Smith, in the U.S., demonstrated that diphtheria toxin neutralized by antitoxin (forming a Toxin-Anti-Toxin complex, TAT) remained immunogenic and eliminated local reactions seen in the modified toxin. For some years, beginning about 1910, TAT was used for active immunization against diphtheria. TAT had two undesirable characteristics as a vaccine. First, the toxin used was highly toxic, and the quantity injected could result in a fatal toxemia unless the toxin was fully neutralized by antitoxin. Second, the antitoxin mixture was horse serum, the components of which tended to be allergenic and to sensitize individuals to the serum. In 1913, Schick designed a skin test as a means of determining susceptibility or immunity to diphtheria in humans. Diphtheria toxin will cause an inflammatory reaction when very small amounts are injected intracutaneously. The Schick Test involves injecting a very small dose of the toxin under the skin of the forearm and evaluating the injection site after 48 hours. A positive test (inflammatory reaction) indicates susceptibility (nonimmunity). A negative test (no reaction) indicates immunity (antibody neutralizes toxin). In 1929, Ramon demonstrated the conversion of diphtheria toxin to its nontoxic, but antigenic, equivalent (toxoid) by using formaldehyde. He provided humanity with one of the safest and surest vaccines of all time-the diphtheria toxoid. In 1951, Freeman made the remarkable discovery that pathogenic (toxigenic) strains of C. diphtheriae are lysogenic, (i.e., are infected by a temperate B phage), while non lysogenized strains are avirulent. Subsequently, it was shown that the gene for toxin production is located on the DNA of the B phage. In the early 1960s, Pappenheimer and his group at Harvard conducted experiments on the mechanism of an action of the diphtheria toxin. They studied the effects of the toxin in HeLa cell cultures and in cell-free systems, and concluded that the toxin inhibited protein synthesis by blocking the transfer of amino acids from tRNA to the growing polypeptide chain on the ribosome. They found that this action of the toxin could be neutralized by prior treatment with diphtheria antitoxin. Subsequently, the exact mechanism of action of the toxin was shown, and the toxin has become a classic model of a bacterial exotoxin.

人类疾病

白喉是一种迅速发展，急性的发热感染，涉及局部和全身性病理学。当地的病变发展上呼吸道涉及上皮细胞坏死损伤。由于这种损伤，血浆泄漏到该区域和纤维蛋白网络形式，其与迅速生长的C.白喉细胞相互界线。该膜状网络覆盖局部病变的部位，称为假膜。白喉杆菌不会倾向于在局部病变部位的表面上侵入下面或远离表面上皮细胞的组织。在该网站上，它们产生通过淋巴通道和血液吸收和散发到身体的敏感组织的毒素。这些组织的退行性变化，包括心脏，肌肉，周围神经，肾上腺，肾脏，肝脏和脾脏，导致疾病的全身病理。在世界各地的白喉仍然发生的地区，它主要是儿童疾病，婴儿期和童年的大多数人都有抗白喉的免疫力。在早些时候，当非视长人口（即美洲原住民）暴露于疾病时，所有年龄段的人都被感染和杀死。

致病性

棒状杆菌白喉杆菌的致病性包括两个不同的现象：1.喉部局部组织的血液，这需要殖民化和随后的细菌增殖。关于该病原体的粘附机制，没有任何熟知的。2.ToxigeNesis：白喉毒素的细菌产生。C. diphtheriae的毒力不能单独归因于毒性，因为明显的侵入性阶段显然是毒性的。然而，由于其在殖民化站点的短程效应，白喉毒素在殖民化过程中发挥了（必要的？）作用。三种植物棒状杆菌菌株被认可，重臂，中间核和脑炎。它们通过下降顺序在这里列出了他们在人类中产生的疾病的严重程度。所有菌株都产生相同的毒素，并且能够殖民化喉部。三种菌株之间的毒力的差异可以通过它们的不同能力来解释产生毒素的速率和数量，并通过其不同的增长率来解释。重臂菌株具有60分钟的产生时间（体外）; the intermedius strain has a generation time of about 100 minutes; and the mitis stain has a generation time of about 180 minutes. The faster growing strains typically produce a larger colony on most growth media. In the throat (in vivo), a faster growth rate may allow the organism to deplete the local iron supply more rapidly in the invaded tissues, thereby allowing earlier or greater production of the diphtheria toxin. Also, if the kinetics of toxin production follow the kinetics of bacterial growth, the faster growing variety would achieve an effective level of toxin before the slow growing varieties.

产毒性

两个因素对白喉棒状杆菌产生白喉毒素的能力有很大的影响:(1)细胞外铁的低浓度和(2)细菌染色体中存在溶源性原噬菌体。产生毒素的基因发生在原噬菌体的染色体上，但一种细菌抑制蛋白控制该基因的表达。阻遏物被铁激活，铁通过这种方式影响毒素的产生。只有在缺铁条件下，溶源细菌才能合成高产量的毒素。铁的作用。在人工培养中，控制毒素产量的最重要因素是培养基中无机铁(Fe++或Fe+++)的浓度。只有在外源铁供应耗尽后，毒素才能高产合成(这对毒素的工业生产产生类毒素具有实际意义。在适当的缺铁条件下，白喉杆菌会合成白喉毒素，为其总蛋白的5% !)据推测，这种现象在体内也会发生。在上呼吸道组织中的铁供应耗尽之前，该细菌可能不会产生最大数量的毒素。 It is the regulation of toxin production in the bacterium that is partially controlled by iron. The tox gene is regulated by a mechanism of negative control wherein a repressor molecule, product of the DtxR gene, is activated by iron. The active repressor binds to the tox gene operator and prevents transcription. When iron is removed from the repressor (under growth conditions of iron limitation), derepression occurs, the repressor is inactivated and transcription of the tox genes can occur. Iron is referred to as a corepressor since it is required for repression of the toxin gene. The role of B-phage. Only those strains of Corynebacterium diphtheriae that that are lysogenized by a specific Beta-phage produce diphtheria toxin. A phage lytic cycle is not necessary for toxin production or release. The phage contains the structural gene for the toxin molecule, since lysogeny by various mutated Beta phages leads to production of nontoxic but antigenically-related material (called CRM for “cross-reacting material”). CRMs have shorter chain length than the diphtheria toxin molecule but cross react with diphtheria antitoxins due to their antigenic similarities to the toxin. The properties of CRMs established beyond a doubt that the tox genes resided on the phage chromosome rather than the bacterial chromosome. Even though the tox gene is not part of the bacterial chromosome the regulation of toxin production is under bacterial control since the DtxR (regulatory) gene is on bacterial chromosome and toxin production depends upon bacterial iron metabolism. It is of some interest to speculate on the role of the diphtheria toxin in the natural history of the bacterium. Of what value should it be to an organism to synthesize up to 5% of its total protein as a toxin that specifically inhibits protein synthesis in eukaryotes (and archaebacteria)? Possibly the toxin assists colonization of the throat (or skin) by killing epithelial cells or neutrophils. There is no evidence to suggest a key role of the toxin in the life cycle of the organism. Since mass immunization against diphtheria has been practiced, the disease has virtually disappeared, and C. diphtheriae is no longer a component of the normal flora of the human throat and pharynx. It may be that the toxin played a key role in the colonization of the throat in nonimmune individuals and, as a consequence of exhaustive immunization, toxigenic strains have become virtually extinct.

白喉毒素的作用方式

白喉毒素是一种双组分的细菌外毒素，合成为含有a(活性)结构域和B(结合)结构域的单链多肽链。毒素与敏感细胞上的特定受体(现在称为HB-EGF受体)结合，并通过受体介导的内吞作用进入细胞。核内体囊泡的酸化导致蛋白质的展开和一段插入到核内体膜中。显然，由于核内体膜上的活性，a亚基在B亚基插入并穿过膜时被裂解并释放出来。一旦进入细胞质，A片段恢复其构象和酶活性。片段A催化adp -核糖从NAD转移到真核延伸因子2，真核延伸因子2抑制后者合成蛋白质的功能。最终，宿主细胞所有EF-2分子的失活导致细胞死亡。ADP核糖基的连接发生在组胺的一种不寻常的衍生物，称为二苯甲酰胺。

白喉毒素的作用方式

体外，天然白喉毒素是无活性的，可以在硫醇存在下通过胰蛋白酶激活。片段A的酶活性在完整的毒素中掩盖。片段B需要将天然毒素与其同源受体结合并允许从内体组逸出。片段B的C末端B含有肽区域，该肽区域将其连接到敏感细胞膜上的HB-EGF受体，N-末端是强疏水区域，该区域将插入膜脂双层中。特异性膜受体，肝素结合表皮生长因子（HB-EGF）前体是多种细胞表面上的蛋白质。细胞上Hb-EGF受体的发生和分布决定了动物物种和动物物种某些细胞对白喉毒素的易感性。通常，HB-EGF前体释放影响正常细胞生长和分化的肽激素。一个假设是Hb-EGF受体本身是蛋白酶，当碎片使其通过内体膜进入细胞质时，蛋白酶缩短碎片并减少其与B片段之间的二硫键桥。

对白喉的免疫力

对白喉的免疫力主要是毒素中和抗体（抗毒素）。UTERO中的被动免疫是在出生后持续到最多1或2年的过程中。在白喉是流行和群众免疫的地区，大多数幼儿对感染的影响非常敏感。可能在保留一些母体免疫的婴儿中的温和或不吸引感染，并且在感染低毒力的成年人（不吸引感染）的成年人中，可以产生积极的免疫力。从白喉完全恢复的个体可能继续留在喉咙或鼻子中的生物周数周甚至几个月。过去，主要是通过这种健康的载体来蔓延，毒性细菌在人口中保持。在儿童群众免疫之前，观察到5％或更高的C. diphtheriae的载体速率。由于儿童的高度高，人工免疫普遍倡导。Toxoid以2或3剂（分开1个月）给药，用于3-4个月的原发性免疫。在一年后，应给予增强剂注射，这是建议在儿童时期施用几种增强剂注射。 Usually, infants in the United States are immunized with a trivalent vaccine containing diphtheria toxoid, pertussis vaccine, and tetanus toxoid (DPT or DTP vaccine).