Abstract
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.
Highlights
Legionella pneumophila is a Gram-negative bacterium commonly found in superficial-water ecosystems and in association with microbial biofilms [1]
sequence type (ST)-1356 was present in 6 locations from BV, with a total of 21 isolates, whereas ST-777 was found in 4 localities, one from Comunidad Valenciana (CV) and three from BV, for a total of 6 isolates
Population Structure In order to investigate the extent and distribution of genetic differentiation among the samples studied, we considered two datasets, one including the L. pneumophila strains isolated from the same watershed (BV), and the other with isolates from different locations in the Comunidad Valenciana (CV)
Summary
Legionella pneumophila is a Gram-negative bacterium commonly found in superficial-water ecosystems and in association with microbial biofilms [1]. It is capable of colonizing urban and industrial water-supply systems, spreading into the environment through aerosols and causing infection when inhaled by susceptible persons. L. pneumophila was first reported as a pathogen after an acute pneumonia outbreak in Philadelphia (USA) during a convention of the American Legion in 1976 [2]. Numerous community- and travel-associated outbreaks of Legionella-associated cases have been reported. Other species of Legionella are capable of producing infection, L. pneumophila serogroup 1 is responsible for about 84% of sporadic cases and outbreaks of legionellosis in the world and The most severe form of pneumonia caused by Legionella infection is known as Legionnaires‘ disease but there is a milder, flu-like form known as Pontiac fever [3].
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