Cooperation and cheating in the evolution of antibiotic resistance in bacteria

描述(申请人提供)：细菌中出现的抗生素耐药性是对公共卫生的持续挑战。β-内酰胺类抗生素，通过抑制 细胞壁合成，既是最古老也是使用最广泛的一类抗生素。细菌可以通过表达内酰胺酶来获得对这些抗生素的抗药性，内酰胺酶会使抗生素失活。抗生素的这种失活可能是一种合作行为，因为整个细胞群体都受益于抗生素的去除。在这项建议中，我们量化了细菌在β-内酰胺类抗生素中生长的合作性质，并探索了这种合作对抗生素耐药性演变的影响。我们假设，将抗生素中合作细菌生长的建模与定量测量相结合，将产生对抗生素耐药性进化的新见解。初步实验已经表征了细菌群体在环境中集体分解抗生素的方式。对这些合作生长动态的建模做出了令人惊讶的但可检验的预测，即关于β-内酰胺酶的哪些突变将在整个种群中传播。我们专注于β-内酰胺酶的突变，使这种酶能够分解一系列临床重要的药物--这种酶的版本被称为超广谱β-内酰胺酶(ESBL)，是一个严重的公共卫生问题。这里描述的方法是PI之前研究微生物进化和种群动力学的实验的自然延伸。三个特定的目标将指导我们对抗生素耐药性的进化动力学的研究：1)确定细菌在β-内酰胺类抗生素中生长的合作性质如何影响选择的方向和导致更具耐药性的突变株的繁殖的条件。2)确定缺乏编码β-内酰胺酶的质粒的敏感细菌是否可以扮演“骗子”的角色，并利用使抗生素失活的耐药细菌。3)探索对单一抗生素耐药的两株细菌在多种药物环境中协同生长的条件。这些研究提供了一套新的定量方法来了解细菌在抗生素存在下的进化动力学。我们期望这些研究将为抗生素耐药性的进化起源提供新的见解，并有助于阐明进化有利于合作行为出现的条件。

DESCRIPTION (provided by applicant): The emergence of antibiotic resistance in bacteria is a persistent challenge to public health. beta-lactam antibiotics, which kill bacteria by inhibiting cell wall synthesis, are both the oldest and most widely used class of antibiotics. Bacteria can gain resistance to these antibiotics by expressing the enzyme lactamase, which inactivates the antibiotic. This inactivation of the antibiotic may be a cooperative behavior because the entire cell population benefits from the removal of the antibiotic. In this proposal we quantify the cooperative nature of bacterial growth in beta-lactam antibiotics and explore the consequences of this cooperation for the evolution of antibiotic resistance. We hypothesize that integrating modeling with quantitative measurements of the cooperative bacterial growth in antibiotics will yield novel insights into the evolution of antibiotic resistance. Preliminary experiments have characterized the manner in which bacterial populations collectively break down antibiotics in the environment. Modeling of these cooperative growth dynamics makes surprising yet testable predictions regarding which mutations in beta-lactamase will spread throughout the population. We focus on mutations in beta-lactamase that allow the enzyme to break down a wide range of clinically important drugs- such versions of the enzyme are called Extended Spectrum beta-Lactamases (ESBL) and are a serious public health concern. The approach described here is a natural extension of the PI's previous experiments studying evolutionary and population dynamics in microbes. Three specific aims will guide our study of the evolutionary dynamics of antibiotic resistance: 1) Determine how the cooperative nature of bacterial growth in beta-lactam antibiotics influences the direction of selection and the conditions that lead to the sprea of more resistant mutants. 2) Determine whether sensitive bacteria, which lack the plasmid encoding beta-lactamase, can act as "cheaters" and take advantage of the resistant bacteria that are inactivating the antibiotic. 3) Explore the conditions in which two bacterial strains, eah resistant to a single antibiotic, can cooperatively grow in a multi-drug environment. These studies present a novel set of quantitative approaches to understand the evolutionary dynamics of bacteria in the presence of antibiotics. We expect that these studies will provide new insight into the evolutionary origin of antibiotic resistance and will also help to clarify the conditions n which evolution can favor the emergence of cooperative behaviors.