Environmental (Saprozoic) Pathogens of Engineered Water Systems: Understanding Their Ecology for Risk Assessment and Management

Abstract

Major waterborne (enteric) pathogens are relatively well understood and treatment controls are effective when well managed. However, water-based, saprozoic pathogens that grow within engineered water systems (primarily within biofilms/sediments) cannot be controlled by water treatment alone prior to entry into water distribution and other engineered water systems. Growth within biofilms or as in the case of Legionella pneumophila, primarily within free-living protozoa feeding on biofilms, results from competitive advantage. Meaning, to understand how to manage water-based pathogen diseases (a sub-set of saprozoses) we need to understand the microbial ecology of biofilms; with key factors including biofilm bacterial diversity that influence amoebae hosts and members antagonistic to water-based pathogens, along with impacts from biofilm substratum, water temperature, flow conditions and disinfectant residual—all control variables. Major saprozoic pathogens covering viruses, bacteria, fungi and free-living protozoa are listed, yet today most of the recognized health burden from drinking waters is driven by legionellae, non-tuberculous mycobacteria (NTM) and, to a lesser extent, Pseudomonas aeruginosa. In developing best management practices for engineered water systems based on hazard analysis critical control point (HACCP) or water safety plan (WSP) approaches, multi-factor control strategies, based on quantitative microbial risk assessments need to be developed, to reduce disease from largely opportunistic, water-based pathogens.

Household proximity to water and nontuberculous mycobacteria in children with cystic fibrosis

“…Despite recent evidence of person‐to‐person transfer of NTM, inhalation secondary to environmental exposure is still considered the main route of transmission . The hydrophobicity of the cell surface of NTM allows it to readily aerosolize from water.…”

“…Nontuberculous mycobacteria (NTM) are ubiquitous in nature and yet only cause detrimental lung disease to select groups of individuals . These non‐motile, aerobic, gram‐positive rods live freely in biofilms on water and soil . There have been over 100 species of NTM identified, but two groups in particular, M. avium‐intracellulare complex (MAC) and Mycobacterium abscessus complex (MABSC), comprise the majority of NTM lung disease in cystic fibrosis (CF) patients in the United States .…”

“…1,2 These non-motile, aerobic, grampositive rods live freely in biofilms on water and soil. [3][4][5][6] There have been over 100 species of NTM identified, but two groups in particular, M. avium-intracellulare complex (MAC) and Mycobacterium abscessus complex (MABSC), comprise the majority of NTM lung disease in cystic fibrosis (CF) patients in the United States. 2,4,6 In the CF population, NTM is an emerging pathogen as its prevalence in the United States has climbed from 1.3% in 1984 to 14% in 2014.…”

Influence of Sampling Season and Sampling Protocol on Detection of Legionella Pneumophila Contamination in Hot Water / Paraugu Ņemšanas Sezonalitātes Un Paraugu Ņemšanas Metodes Ietekme Uz Legionella Pneumophila Kontaminācijas Noteikšanu Karstajš Ūdenī

“…pneumophila is an opportunistic environmental (Saprozoic) pathogen of engineered water systems (Ashbolt, 2015;Falkinham, 2015), that can reach human lungs via inhalation of contaminated aerosols (Anonymous, 2007) or aspiration of water containing the bacteria (Fields, 2002). Clinical manifestations of the legionellosis vary from mild fever (Pontiac's fever) to potentially lethal pneumonia (Legionnaire's disease) (Stout et al, 1992).…”

Cost of care for hospitalized patients with pulmonary mycobacterial diseases in the United States.

“…370,371 Further, some researchers have suggested that NTM is a result of the progress of modern societies as the disease is transmitted through the public water distribution infrastructure. 372 Another possible pathway for NTM infection is in the food supply. 373 In the US, the undesired outcome for policymakers is NTM infection.…”