Genomics and Health Joint Unit CSISP, FISABIO-University of Valencia/Cavanilles Institute, Valencia, Spain.
PLoS One. 2013 Apr 25;8(4):e61564. doi: 10.1371/journal.pone.0061564. Print 2013.
Legionella pneumophila infects humans to produce legionellosis and Pontiac fever only from environmental sources. In order to establish control measures and study the sources of outbreaks it is essential to know extent and distribution of strain variants of this bacterium in the environment. Sporadic and outbreak-related cases of legionellosis have been historically frequent in the Comunidad Valenciana region (CV, Spain), with a high prevalence in its Southeastern-most part (BV). Environmental investigations for the detection of Legionella pneumophila are performed in this area routinely. We present a population genetics study of 87 L. pneumophila strains isolated in 13 different localities of the BV area irrigated from the same watershed and compare them to a dataset of 46 strains isolated in different points of the whole CV. Our goal was to compare environmental genetic variation at two different geographic scales, at county and regional levels. Genetic diversity, recombination and population structure were analyzed with Sequence-Based Typing data and three intergenic regions. The results obtained reveal a low, but detectable, level of genetic differentiation between both datasets, mainly, but not only, attributed to the occurrence of unusual variants of the neuA locus present in the BV populations. This differentiation is still detectable when the 10 loci considered are analyzed independently, despite the relatively high incidence of the most common genetic variant in this species, sequence type 1 (ST-1). However, when the genetic data are considered without their associated geographic information, four major groups could be inferred at the genetic level which did not show any correlation with sampling locations. The overall results indicate that the population structure of these environmental samples results from the joint action of a global, widespread ST-1 along with genetic differentiation at shorter geographic distances, which in this case are related to the common watershed for the BV localities.
嗜肺军团菌仅从环境来源感染人类引起军团病和庞蒂亚克热。为了制定控制措施并研究暴发的来源，了解这种细菌在环境中的菌株变体的范围和分布至关重要。历史上，西班牙巴伦西亚社区（CV）地区的军团病散发和暴发相关病例频繁发生，其最东南部（BV）地区的患病率很高。该地区常规进行环境调查以检测嗜肺军团菌。我们对来自同一流域灌溉的 BV 地区 13 个不同地点分离的 87 株嗜肺军团菌进行了群体遗传学研究，并将其与整个 CV 不同地点分离的 46 株菌株数据集进行了比较。我们的目标是比较两种不同地理尺度（县和地区）的环境遗传变异。使用基于序列的分型数据和三个基因间区域分析遗传多样性、重组和种群结构。结果表明，两个数据集之间存在低但可检测到的遗传分化，主要归因于在 BV 人群中存在 neuA 基因座的异常变体，但不仅如此。当分析 10 个考虑的基因座时，尽管该物种最常见的遗传变体序列类型 1（ST-1）的发生率相对较高，但仍可检测到这种分化。然而，当不考虑其相关地理信息而考虑遗传数据时，可以推断出在遗传水平上存在四个主要群体，它们与采样地点没有任何关联。总体结果表明，这些环境样本的种群结构是由广泛分布的 ST-1 以及较短地理距离的遗传分化共同作用的结果，在这种情况下，遗传分化与 BV 地点的共同流域有关。
