Hi all…we’re all well aware of the presence of Legionella in ‘built environments’ and their status as a human pathogen but we know very little about their presence in source water used for drinking water. A study which has just appeared in mSphere fills in some of those knowledge gaps. I found it interesting that the relative abundance of Legionella and Amoebozoa, some of which are natural hosts of legionellae, tended to be higher in pristine sites than in sites affected by agricultural activity.
The authors conclude “While the presence of Legionella spp. in natural water samples alone is not a significant public health concern, these organisms may seed human-made water systems. In turn, these systems could become sources of Legionella dissemination under permissive conditions. Understanding the diversity of organisms present in the natural aquatic environment and factors that may contribute to increased abundance of specific Legionella spp. in these environments may help public health workers identify potential new threats to human health and respond quickly to LD by using improved diagnostic and typing assays. This study demonstrates that natural aquatic environments, including watersheds, likely harbor previously unrecognized Legionella spp. As culture-independent diagnostic tests for LD become more commonly utilized, it will be important to evaluate the ability of these assays to detect new and emerging Legionella spp. and assess their potential to cause disease.”
Bill
Characterization of Legionella Species from Watersheds in British Columbia, Canada
Michael A. Peabody, Jason A. Caravas, Shatavia S. Morrison, Jeffrey W. Mercante, Natalie A. Prystajecky, Brian H. Raphael, Fiona S. L. Brinkman
mSphere July/August 2017 Volume 2 Issue 4 e00246-17
http://msphere.asm.org/content/2/4/e00246-17
ABSTRACT Legionella spp. present in some human-made water systems can cause Legionnaires’ disease in susceptible individuals. Although legionellae have been isolated from the natural environment, variations in the organism’s abundance over time and its relationship to aquatic microbiota are poorly understood. Here, we investigated the presence and diversity of legionellae through 16S rRNA gene amplicon and metagenomic sequencing of DNA from isolates collected from seven sites in three watersheds with varied land uses over a period of 1 year. Legionella spp. were found in all watersheds and sampling sites, comprising up to 2.1% of the bacterial community composition. The relative abundance of Legionella tended to be higher in pristine sites than in sites affected by agricultural activity. The relative abundance levels of Amoebozoa, some of which are natural hosts of legionellae, were similarly higher in pristine sites. Compared to other bacterial genera detected, Legionella had both the highest richness and highest alpha diversity. Our findings indicate that a highly diverse population of legionellae may be found in a variety of natural aquatic sources. Further characterization of these diverse natural populations of Legionella will help inform prevention and control efforts aimed at reducing the risk of Legionella colonization of built environments, which could ultimately decrease the risk of human disease.
IMPORTANCE: “Many species of Legionella can cause Legionnaires’ disease, a significant cause of bacterial pneumonia. Legionella in human-made water systems such as cooling towers and building plumbing systems are the primary sources of Legionnaires’ disease outbreaks. In this temporal study of natural aquatic environments, Legionella relative abundance was shown to vary in watersheds associated with different land uses. Analysis of the Legionella sequences detected at these sites revealed highly diverse populations that included potentially novel Legionella species. These findings have important implications for understanding the ecology of Legionella and control measures for this pathogen that are aimed at reducing human disease.”
