Targeting airborne bacterial infection: Studies on patient- and laboratory-generated mycobacterium tuberculosis aerosols.

在全球范围内，结核病是由细菌引起的死亡和疾病的最重要的单一原因。像许多其他影响肺部的细菌感染一样，结核病通过被感染者产生的气溶胶（咳嗽和其他呼吸道活动排出的微小飞沫）传播。结核病和其他空气传播的细菌感染每年在全世界造成大约400万人死亡，这在英国仍然是一个重大问题。尽管气溶胶在传播感染方面很重要，但我们对细菌需要通过这种途径传播的生物学特性知之甚少。我们以前的研究表明，结核病例排出的细菌的特性是独特的，并且它们可能在运输过程中进一步改变。我们最近建立了捕获结核病患者产生的气溶胶的方法，并确定其细菌病因结核分枝杆菌（Mtb）表达的基因模式。这些方法是建立在患者咳嗽气雾剂采样系统（CASS）的基础上的，该系统显示，家庭接触者感染结核病的风险可以通过患者在标准CASS样本中产生的细菌数量来预测。我们在这里使用CASS系统将使我们能够将我们的结果与我们取样的个体患者的传染性联系起来。在这里，我们将描述CASS和实验室气溶胶产生和采样系统，并使用两者来回答四个问题：1)结核病气溶胶不仅仅是患者咳嗽的粘液分泌物（痰）的简单样本（痰分析传统上用于评估传染性）；2)实验室气溶胶中结核分枝杆菌的存活和基因表达如何随时间和环境条件变化；3)哪些结核分枝杆菌基因对结核分枝杆菌在气溶胶中的存活和转移起重要作用；4)标准琼脂培养方法是否低估了气溶胶中结核分枝杆菌的数量？通过定义结核分枝杆菌基因和对气溶胶传播重要的基因表达模式，我们的目标是发现控制感染的新方法；这些措施可能包括针对患者体内关键的结核分枝杆菌基因产物，使其降低传染性，改变环境条件，使其不利于结核分枝杆菌的生存和传播，以及预防新感染的发生。减少传染性对于管理日益严重的耐药结核病问题可能特别重要，因为耐药结核病可能需要很长时间才能使患者不再具有传染性。对环境条件的简单改变可能对医疗保健设施的管理很有价值，这在资源有限的环境中是一个特别的问题。最后，结核分枝杆菌在气溶胶转移中改变其特性的可能性增加了这样一种可能性，即我们不知道当一个新的潜在受害者吸入这种细菌时，它表现出什么特征，以及这些特征中哪些是建立感染所必需的。通过确定结核分枝杆菌适应气溶胶转移的方式，我们的工作具有明确的潜力，可以为最近暴露的个体确定新的结核分枝杆菌预防治疗靶点，以及可能预防感染的疫苗，这是目前卡介苗和正在开发的候选疫苗的一个特别薄弱的特点。我们的研究涉及临床医生（比勒陀利亚），细菌学家（莱斯特），以及气溶胶生物学（波顿）和物理学（利兹）专家之间的合作。我们将利用南非、莱斯特和英国公共卫生部（波顿）的特殊设施来开展这项工作。利兹大学的研究小组将开发我们采样系统的计算机模型，以更好地定义采样结果对气溶胶的完全反映程度。这些和我们的生物学结果将用于开发新的患者传染性定量模型。我们相信，了解结核气雾剂将为控制结核杆菌创造新的机会，并提供适用于其他空气传播感染的重要经验教训。

Globally, tuberculosis (TB) is the single most important cause of death and disease due to a bacterial agent. Like many other bacterial infections affecting the lungs, TB is transmitted by aerosols (tiny droplets expelled by coughing and other respiratory efforts) generated by infected individuals. Together TB and other airborne bacterial infections cause approximately 4 million deaths worldwide every year and remain a significant problem in the UK. In spite of the importance of aerosols in transmitting infection we have very little information on the biological properties that bacteria need to be transmitted by this route. Our previous research suggests both that the properties of bacteria expelled by TB cases are distinctive and that they are likely to change further during transit. We recently established methods for capturing aerosols produced by TB patients and to determine the pattern of genes expressed by its bacterial cause, Mycobacterium tuberculosis (Mtb). These methods are built on the patient Cough Aerosol Sampling System (CASS) which has revealed that the risk of infection in household contacts of a TB can be predicted by the number bacteria the patient produces in a standard CASS sample. Our use of the CASS system here will enable us to relate our results to the infectiousness of the individual patients we sample.Here we will characterise the CASS and a laboratory aerosol generation and sampling system, and use both to answer four questions: 1) is the TB aerosol more than just a simple sample of the mucus secretions (sputum) patients cough-up (sputum analysis has traditionally been used to assess infectiousness); 2) how does survival and gene expression of Mtb change with time and ambient conditions in laboratory aerosols; 3) which of Mtb's genes make important contributions to the bacterium's survival and transfer in aerosol; and 4) are the numbers of Mtb bacilli in aerosols underrepresented by standard agar culture methods? By defining the Mtb genes and gene expression patterns important for aerosol transmission we aim to uncover new methods to control infection; these could include targeting critical Mtb gene products in patients to render them less infectious, altering ambient conditions to make them unfavourable for survival and transmission of Mtb and preventing the establishment of new infections. Reducing infectiousness could be particularly important in managing the increasing problem of drug resistant TB, where it may take a long time to render patients non-infectious. Simple alterations to ambient conditions could be valuable in the management of healthcare facilities, a particular problem in resource-limited settings. Finally, the potential for Mtb to change its properties in response to aerosol transfer raises the likelihood that we do not know what features the bacterium expresses when it is breathed in by a new potential victim and which of these features is essential to establishing infection. By identifying the way Mtb adapts to aerosol transfer, our work has clear potential to identify new Mtb targets for prophylactic therapy in recently exposed individuals and for vaccines that might prevent infection, a particularly weak feature of the current BCG vaccine and vaccine candidates in development.Our study involves collaborations between clinicians (Pretoria), bacteriologists (Leicester), and specialists in the biology (Porton) and physics (Leeds) of aerosols. We will use exceptional facilities in South Africa, Leicester and Public Health England (Porton) to deliver the work. The Leeds group will develop computer models of our sampling systems to better define how completely the results reflect the aerosols sampled. These and our biological results will be used to develop new quantitative models of patient infectiousness. We believe that understanding the TB aerosol will create new opportunities to control Mtb and provide important lessons applicable to other airborne infections.