Biogeography and Environmental Drivers of Legionella pneumophila Abundance and Genotype Composition across the West Bank: Relevance of a Genotype-Based Ecology for Understanding Legionella Occurrence

Abstract

The West Bank can be considered as a high-risk area for <i>Legionella</i> prevalence in drinking water due to high ambient temperature, intermittent water supply, frequent pressure loss, and storage of drinking water in roof containers. To assess occurrence of <i>Legionella</i> species, especially <i>L. pneumophila</i>, in the drinking water of the West Bank, the drinking water distribution systems of eight hospitals were sampled over a period of 2.3 years covering the seasonal cycle and the major geographic regions. To gain insight into potential environmental drivers, a set of physico-chemical and microbiological parameters was recorded. Sampling included drinking water and biofilm analyzed by culture and PCR-based methods. Cultivation led to the isolation of 180 strains of <i>L. pneumophila</i> that were genotyped by Multi-Locus Variable Number of Tandem Repeat Analysis (MLVA). Surprisingly, the abundance of culturable <i>L. pneumophila</i> was low in drinking water of the sampling sites, with only three out of eight sites where <i>Legionella</i> was observed at all (range: 30-500 CFU/liter). By contrast, biofilm and PCR-based analyses showed a higher prevalence. Statistical analyses with physico-chemical parameters revealed a decrease of <i>L. pneumophila</i> abundance for water and biofilm with increasing magnesium concentrations (>30 mg/l). MLVA-genotype analysis of the <i>L. pneumophila</i> isolates and their spatial distribution indicated three niches characterized by distinct physico-chemical parameters and inhabited by specific consortia of genotypes. This study provides novel insights into mechanisms shaping <i>L. pneumophila</i> populations and triggering their abundance leading to an understanding of their genotype-specific niches and ecology in support of improved prevention measures.