Spatial Epidemiology & Ecology Research Laboratory, Department of Geography, University of Florida, Gainesville, Florida, United States of America.
Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
PLoS Biol. 2020 Dec 28;18(12):e3001052. doi: 10.1371/journal.pbio.3001052. eCollection 2020 Dec.
Bacillus anthracis, a spore-forming gram-positive bacterium, causes anthrax. The external surface of the exosporium is coated with glycosylated proteins. The sugar additions are capped with the unique monosaccharide anthrose. The West African Group (WAG) B. anthracis have mutations rendering them anthrose deficient. Through genome sequencing, we identified 2 different large chromosomal deletions within the anthrose biosynthetic operon of B. anthracis strains from Chile and Poland. In silico analysis identified an anthrose-deficient strain in the anthrax outbreak among European heroin users. Anthrose-deficient strains are no longer restricted to West Africa so the role of anthrose in physiology and pathogenesis was investigated in B. anthracis Sterne. Loss of anthrose delayed spore germination and enhanced sporulation. Spores without anthrose were phagocytized at higher rates than spores with anthrose, indicating that anthrose may serve an antiphagocytic function on the spore surface. The anthrose mutant had half the LD50 and decreased time to death (TTD) of wild type and complement B. anthracis Sterne in the A/J mouse model. Following infection, anthrose mutant bacteria were more abundant in the spleen, indicating enhanced dissemination of Sterne anthrose mutant. At low sample sizes in the A/J mouse model, the mortality of ΔantC-infected mice challenged by intranasal or subcutaneous routes was 20% greater than wild type. Competitive index (CI) studies indicated that spores without anthrose disseminated to organs more extensively than a complemented mutant. Death process modeling using mouse mortality dynamics suggested that larger sample sizes would lead to significantly higher deaths in anthrose-negative infected animals. The model was tested by infecting Galleria mellonella with spores and confirmed the anthrose mutant was significantly more lethal. Vaccination studies in the A/J mouse model showed that the human vaccine protected against high-dose challenges of the nonencapsulated Sterne-based anthrose mutant. This work begins to identify the physiologic and pathogenic consequences of convergent anthrose mutations in B. anthracis.
炭疽芽孢杆菌是一种形成孢子的革兰氏阳性细菌，可引起炭疽病。外孢子的外表面覆盖有糖基化蛋白。糖的添加物由独特的单糖炭疽醇封顶。西非组（WAG）炭疽芽孢杆菌的突变使其缺乏炭疽醇。通过基因组测序，我们在来自智利和波兰的炭疽芽孢杆菌菌株的炭疽醇生物合成操纵子中发现了 2 个不同的大染色体缺失。计算机分析在欧洲海洛因使用者中的炭疽爆发中鉴定出了一株缺乏炭疽醇的菌株。缺乏炭疽醇的菌株不再局限于西非，因此我们研究了炭疽芽孢杆菌 Sterne 中炭疽醇在生理和发病机制中的作用。炭疽醇的缺失延迟了孢子的萌发并增强了孢子的形成。缺乏炭疽醇的孢子比具有炭疽醇的孢子更容易被吞噬，这表明炭疽醇可能在孢子表面发挥抗吞噬作用。与野生型和互补炭疽芽孢杆菌 Sterne 相比，炭疽醇突变体的半数致死量（LD50）降低，死亡时间（TTD）缩短。在 A/J 小鼠模型中感染后，炭疽醇突变体细菌在脾脏中的丰度更高，表明 Sterne 炭疽醇突变体的传播增强。在 A/J 小鼠模型中，样本量较小的情况下，经鼻腔或皮下途径感染 ΔantC 的小鼠的死亡率比野生型高 20%。竞争指数（CI）研究表明，缺乏炭疽醇的孢子比互补突变体更广泛地传播到器官。使用小鼠死亡率动态模型进行死亡过程建模表明，更大的样本量将导致缺乏炭疽醇的感染动物的死亡率显著增加。该模型通过用孢子感染 Galleria mellonella 进行了测试，并证实炭疽醇突变体具有更高的致死性。在 A/J 小鼠模型中的疫苗接种研究表明，人类疫苗可预防非包裹型基于 Sterne 的炭疽醇突变体的高剂量挑战。这项工作开始确定炭疽芽孢杆菌中炭疽醇突变的生理和发病后果。
