From Many Hosts, One Accidental Pathogen: The Diverse Protozoan Hosts of Legionella

Abstract

The 1976 outbreak of Legionnaires' disease led to the discovery of the intracellular bacterial pathogen Legionella pneumophila. Given their impact on human health, Legionella species and the mechanisms responsible for their replication within host cells are often studied in alveolar macrophages, the primary human cell type associated with disease. Despite the potential severity of individual cases of disease, Legionella are not spread from person-to-person. Thus, from the pathogen's perspective, interactions with human cells are accidents of time and space—evolutionary dead ends with no impact on Legionella's long-term survival or pathogenic trajectory. To understand Legionella as a pathogen is to understand its interaction with its natural hosts: the polyphyletic protozoa, a group of unicellular eukaryotes with a staggering amount of evolutionary diversity. While much remains to be understood about these enigmatic hosts, we summarize the current state of knowledge concerning Legionella's natural host range, the diversity of Legionella-protozoa interactions, the factors influencing these interactions, the importance of avoiding the generalization of protozoan-bacterial interactions based on a limited number of model hosts and the central role of protozoa to the biology, evolution, and persistence of Legionella in the environment.

A Novel Legionella Genomic Island Encodes a Copper-Responsive Regulatory System and a Single Icm/Dot Effector Protein Transcriptionally Activated by Copper

“…L egionella pneumophila is an intracellular human pathogen that multiplies within alveolar macrophages and causes a severe pneumonia known as Legionnaires' disease (1)(2)(3). In the environment, L. pneumophila thrives in many different protozoan cells (4)(5)(6), which serve as its training grounds for pathogenesis (7). Inside its eukaryotic host cells, the bacterium remodels its phagosome to generate the Legionella-containing vacuole (LCV) (8,9).…”

Evolution and function of bacterialRCC1repeat effectors

“…Free‐living protozoa represent a privileged environmental niche of Legionella species. While some protozoa kill and digest L. pneumophila (Amaro, Wang, Gilbert, Anderson, & Shuman, 2015; Boamah, Zhou, Ensminger, & O'Connor, 2017), there is indeed a tremendous diversity of environmental hosts, and L. pneumophila has been shown to replicate in at least 30 different protozoan species, including amoebae (e.g., Acanthamoeba , Hartmanella , Naegleria , Vahlkampfia and Dictyostelium spp.) and ciliates (e.g., Tetrahymena and Paramecium spp.…”

Bioaugmentation for the treatment of waterborne pathogen contamination water

“…L. pneumophila, mostly growing inside free-living protozoa feeding on biofilms, results competitive advantage for its survival. Living inside the protozoan host is advantageous for bacteria in many ways like it can defend against phagocytic destruction and get protected from adverse environmental conditions, nutrient-rich growing condition, and water disinfection procedures (Boamah et al, 2017). For controlling such type of resistant waterborne pathogenic bacteria such as L. pneumophila, use of a new natural active antibacterial agent proved to be a promising strategy.…”