Author: Claire Hayward
Hayward, Claire, 2025 Controlling waterborne antimicrobial resistant healthcare associated infections, Flinders University, College of Science and Engineering
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Opportunistic premise plumbing pathogens (OPPPs) are an emerging public health threat. These are waterborne pathogens share characteristics such as biofilm formation, survival in low nutrient environments, disinfectant resistance and growth in amoeba hosts that enable them to persist in drinking water plumbing systems. Globally, the incidence of OPPP healthcare associated infections (HAI) is increasing, and the significance and severity of these infections is also increasing due to the rise in antimicrobial resistance.
The aim of this thesis was to explore factors influencing OPPPs in Australian hospital and residential drinking water plumbing systems. This included investigating prevalence, antimicrobial resistance, interactions with protozoan hosts and the effects of factors such as building type, product design, and plumbing materials on the growth and proliferation of these pathogens. The data presented in this thesis can be used to inform future guidelines to mitigate infection risks in healthcare and residential environments.
A systematic literature review found that residential buildings are often overlooked as a source of waterborne infections. However, they are significant reservoirs for OPPPs such as Legionella pneumophila, Pseudomonas aeruginosa, Acinetobacter baumannii and Mycobacterium avium complex (MAC). These environments were also found to harbor non-waterborne pathogens such Staphylococcus aureus and Enterobacteriaceae, challenging the traditional focus of guidelines that prioritize healthcare facilities and traditionally waterborne bacteria.
Molecular surveillance of Australian hospitals and residential drinking water plumbing systems revealed widespread colonisation by P. aeruginosa (41%), S. aureus (26%), Legionella spp. (26%), L. pneumophila (24%), and A. baumannii (14%). Residential properties had a statistically higher prevalence of OPPPs, particularly associated with biofilm colonization. Additionally, drain biofilms were identified as the primary reservoirs for key antimicrobial resistant (AMR) threats identified by the World Health Organization (WHO) and Centers for Disease Control and Prevention including carbapenem resistant A. baumannii and P. aeruginosa, and methicillin resistant S. aureus. This study is the first to explore these risks within Australian healthcare and residential settings, providing insights into the role of drain biofilms as hidden contributors to the global AMR crisis. However, the influence of building characteristics, including stagnation, hot water system type, and building age, on pathogen prevalence was inconsistent, underscoring the complexity of these environments. A complementary 16S rRNA analysis of biofilms from hospital and residential handwashing basins revealed diverse prokaryotic communities, with high abundances of potentially corrosive, biofilm-forming, and pathogenic genera, including those not typically waterborne. β-diversity analysis showed a statistically significant difference in bacterial communities between building types (hospital vs. residential, p = 0.0415). However, in hospitals, there was no significant difference between drain and faucet biofilms, suggesting that microbial communities are highly similar between these two sites. This study highlights the potential mechanisms of microbial transfer between these sites and discusses how interventions aimed at one site could influence the microbial dynamics of the other.
Handwashing basins were identified as a niche for diverse OPPP communities in the earlier stages of this thesis. These findings informed the development of a model system designed to investigate transmission pathways, including aerosolization and retrograde contamination, under controlled conditions. This model demonstrated that lower flow rates led to increased aerosol production from contaminated drains (p=0.021) and greater retrograde contamination from the drain up to the faucet compared to higher flow rates. This suggests that water-saving recommendations, which often promote lower flow rates, may inadvertently increase the risk of microbial transmission. This is particularly concerning in healthcare settings, where infection control must take precedence over water conservation goals. Future guidelines must consider the potential conflict between infection control measures and water-saving initiatives, particularly for vulnerable populations in hospital or home healthcare settings.
To understand the potential public health implications of a legislative change promoting a shift away from brass to "lead-free" alternative plumbing materials such as stainless steel, a laboratory model study investigated the effects of plumbing materials on biofilm formation, OPPP growth, and lead leaching under stagnant conditions. Bioreactors inoculated with A. baumannii, P. aeruginosa, MAC, and Acanthamoeba polyphaga were analysed using selective culture and viability-based flow cytometry. Each OPPP responded differently to brass and stainless steel, with brass exhibiting greater antimicrobial activity. However, both materials leached lead above WHO guidelines after 10 weeks of stagnation, with stainless steel showing lead deposits likely from post manufacturing contamination. These results emphasize the importance of evidence-based plumbing material selection that considers both microbial and chemical risks.
This research advocates for a dynamic multi-barrier approach to OPPP surveillance and drinking water treatment, emphasizing the need for evidence-based, multidisciplinary regulatory decisions to effectively control AMR waterborne HAIs. Collaboration between microbiologists, engineers, and public health professionals with inform future guidelines to better protect vulnerable individuals and improve water quality.
Keywords: Opportunistic premise plumbing pathogens, drinking water, biofilm, disinfectant resistance, antimicrobial resistance
Subject: Microbiology & Infectious Diseases thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Science and Engineering
Supervisor: Harriet Whiley