Ecological population structure and emergence of virulent Vibrio parahaemolyticus

描述（由申请人提供）：许多传染病是由非致病性物种中的少数菌株引起的，但驱动其出现的生态和种群遗传机制尚不清楚。鉴于与气候和土地利用变化有关的许多流行病日益频繁，了解这些动态尤为重要。例如，在美国大部分地区，由受污染的贝类引起的疾病相对较少，但发病率正在上升，并开始与较温暖的国家平行。副溶血性弧菌（Vp）的丰度与水温较高、盐度适中的水体呈正相关。然而，这些生态变量并不能充分预测副病毒的流行，部分原因是潜在致病性副病毒的相对丰度远难以预测。本项目旨在确定和量化影响有毒副Vp在牡蛎中相对流行的生态因素。我们的模型研究区域，新罕布什尔州的大海湾河口，是理想的，因为在相对较小的空间尺度上发生的环境条件范围很广，而且因为它的温暖水域促进了通常与温暖气候相关的物种。已知副溶血性弧菌与其他致病性弧菌一起居住在该河口，并且已经有几例急性副溶血性弧菌感染来自河口，这表明少数致病性菌株居住在社区中。我们的重点问题是：环境因素是如何驱动Vp种群动态的？我们假设副毒株在毒力性状上的变化与某些环境变量有关，例如气候的波动会特别影响副毒株的相对丰度。我们的假设是基于我们的初步数据，这些数据显示高细胞毒性菌株的流行与温度升高之间存在显著的相关性。利用多位点序列分型分析（MLST）对河口分离株的种群结构和重组程度进行了研究。到目前为止，我们的初步遗传分型表明，在具有三个不同Vp群体的群落中存在显着的遗传交换。所提出的研究与已发表的研究相比是独特的，特别是1)包含了不同的自然种群（不仅仅是具有特定毒力标记的子集），2)一个遗传分型方案，包括已知和假定的毒力基因，并允许检测种群内的毒力基因转移，3)它包括功能毒力的表征，将覆盖在分子分型方案上。我们有两个具体的目标来解决以下问题：环境因素是否影响牡蛎中天然Vp种群的毒力潜力？北方Vp群体的遗传结构是什么？致病因子是如何与这种结构联系起来的？公共卫生相关性：最近在较冷的北方气候地区爆发的副溶血性弧菌疫情与大流行克隆菌无关，而与具有独特遗传成分的独特常驻细菌有关，这可能预示着全球气候变化对人类健康的风险日益增加。评估感染风险和制定预防方案的一个主要障碍是缺乏对在天然副溶血性弧菌种群中导致毒性生物变体出现的因素的了解。在河口生态的背景下，结合分子分型和毒力评估将为这种新出现的病原体产生预测模型提供宝贵的见解。

DESCRIPTION (provided by applicant): Numerous infectious diseases are caused by minority strains within otherwise nonpathogenic species, but the ecological and population genetic mechanisms that drive their emergence remains unclear. Understanding these dynamics is especially important in light of the increasing frequency of many epidemics tied to changes in climate and land use. For example, illness caused by contaminated shellfish is relatively infrequent in most of the U.S. but incidence is on the rise and beginning to parallel that of warmer countries. The abundance of the major causative bacterium Vibrio parahaemolyticus (Vp) is positively correlated with warmer waters with moderate salinity. Yet these ecological variables do not sufficiently predict Vp epidemics in part because the relative abundance of potentially pathogenic Vp is far less predictable. This project seeks to identify and quantify the ecological factors that influence the relative prevalence of virulent Vp in oysters. Our model study area, the Great Bay estuary of New Hampshire, is ideal because of the wide range of environmental conditions that occur over relatively small spatial scales, and because its warmer waters promote species typically associated with warmer climates. Vp are known to reside in this estuary along with other pathogenic Vibrios and there have been several acute Vp infections from the estuary suggesting that minority pathogenic strains are resident in the community. Our focal question is: how do environmental factors drive the population dynamics of Vp? We hypothesize that Vp strains that vary in virulence traits are associated with certain environmental variables, such that fluctuations in climate will specifically influence the relative abundance of virulent Vp. We base this hypothesis on our preliminary data that shows a significant correlation between the prevalence of highly cytotoxic strains and increased temperature. Using multi-locus sequence typing analysis (MLST), we will examine the population structure and extent of recombination between estuary isolates. Our preliminary genetic typing thus far suggests that there is significant genetic exchange within the community that has three distinct Vp populations. The proposed study is unique from those published, specifically by 1) the inclusion of the diverse natural population (not only a subset with specific virulence markers), 2) a genetic typing scheme that includes known and putative virulence genes and allows the detection of virulence gene transfer within the population, and 3) it includes a characterization of functional virulence that will be overlaid upon the molecular typing scheme. We have two specific aims that address the following questions: Do environmental factors influence the virulence potential of natural Vp populations in oysters? What is the genetic structure of northern Vp populations and how are pathogenic elements linked to this structure? PUBLIC HEALTH RELEVANCE: Recent major outbreaks of Vibrio parahaemolyticus in cooler northern climes have been linked not to the pandemic clone, but to distinct resident bacteria of unique genetic composition, perhaps foreshadowing the increasing risk to human health due to global climate change. A major obstacle to assessing risk of infection and developing preventative protocols is a lack of understanding of what factors contribute to the emergence of virulent biovars within natural V. parahaemolyticus populations. The combined molecular typing and virulence assessment in the context of estuarine ecology will provide invaluable insight necessary to generate predictive models for this emerging pathogen.