IWA Publishing in conjunction with the International Water Association’s Young Water Professionals is happy to announce a new initiative spotlighting the work of Young Water Professionals and showing how the work published in IWA Publishing Journals can be useful to those beginning their careers in the water sector. 

Our sixth spotlight blog is from Casey Huang, a PhD student based at the Advanced Water Management Centre (AWMC), at the University of Queensland, Australia. You can connect with Casey on LinkedIn.

Casey had access to our entire journal portfolio for one month, and picked out some interesting papers to discuss, read her thoughts below! A big thank you to Casey for participating! 

Mysteries of a bacterial pathogen: Legionella in water systems

Hello! I’m Casey, a PhD student based at the Advanced Water Management Centre (AWMC), at the University of Queensland in Australia. I was fortunate to be invited by IWA Publishing to access their journals and research papers, and I hope I can share some insight or maybe even a bit of inspiration to tackle your own research questions in this blog post today.

I’ve always had a huge fascination with microbiology – these microscopic organisms can’t be easily seen by the naked eye, yet can be found all around us. Whether it’s in food, in our indoor spaces, in the outdoor environment and surroundings, or even within our bodies, microbes can be both helpful and harmful with many mysteries yet to be unravelled. This led me to pursue a project in environmental microbiology, where I’m currently working on a project exploring the ecology and control of waterborne bacterial pathogen, Legionella spp., in the context of drinking water systems.

From source to tap, drinking water quality can degrade in drinking water distribution systems (DWDS), particularly at the premise plumbing portion of the system (i.e. within buildings, such as cold and hot water, and outlets such as showers and taps). This may be due to biological contaminants like microorganisms forming biofilms – akin to microbial cities within these systems, thus creating a favourable environment for opportunistic premise plumbing pathogens (OPPPs) like Legionella, to persist and thrive. These OPPPs can then be transmitted through contaminated aerosols released by drinking water outlets to downstream consumers and the vulnerable population in healthcare settings, leading to severe health implications. Much of the research has focused on the pathogenesis and infection caused by Legionella spp., as well as drinking water studies using model systems such as pilot-scale or laboratory-scale reactors. However, there are still many complex questions to be addressed in real systems – such as with relation to microbial diversity and function (i.e. who is there and what are they doing?), health risks associated with their occurrence, as well as the what are the roles of various physical/biological/chemical influences together combined in these environments.

The complexity involved with the detection and monitoring of a cross section of OPPPs in these systems and the various methodologies have been comprehensively reviewed by Wang et al. (2017). In this review, three major detection methods were explored, ranging from (i) traditional culture-based diagnostics which are typically used by regulators, (ii) culture-independent or molecular methods (such as quantitative polymerase chain reaction (qPCR) and next generation community sequencing), as well as (iii) phenotypic assays. An important aspect that was highlighted in the review was the advantages and limitations of each of the methods, such as addressing cells that may enter a viable but non-culturable state (VBNC). This refers to a survival strategy where viable cells lose their culturability via standard culture-based methods when induced by stressors, such as under nutrient starvation and being exposed to disinfectants such as chlorine.

However, little is known about the underlying physiological processes as well as the virulence or cells in a VBNC state. Dietersdorfer et al. (2018) explores the concept of VBNC Legionella strains further by testing experimental infections models set up with various human macrophages and amoeba as their protozoan hosts. Although infection occurred at a reduced efficacy than their culturable counterparts, VBNC Legionella were still able to infect their various hosts in these infection models. This leaves an open-ended question with relation to how this outcome translates to human infections in vivo, as well as the possibility to underestimate the quantity of infectious Legionella when relying solely on culture-based diagnostics. On the other hand, the aforementioned molecular methods such as qPCR is unable to discriminate between live/damaged/dead cells and the pathogenic status (i.e. detects for “total” Legionella), thus further developments (such as the applicability of novel molecular methods such as viability qPCR) are currently ongoing to address these challenges. Many researchers have advocated for the development of a unified approach for the detection and monitoring of OPPPs, or a combination of various methods for a collective perspective.

Aside from the specific detection and monitoring of OPPPs like Legionella, the rapid advancement of technologies and tools such as next generation sequencing (NGS) via 16S rRNA gene amplicon sequencing has greatly accelerated our understanding of microbial ecology and associated OPPPs in drinking water systems with relation to diversity and function. OPPPs co-exist with biofilms in these systems, and De Sotto et al. (2020) further explored this in residential premise plumbing systems in Singapore by drawing correlations to various factors, where pipe material, age of property and temperature had a significant influence on the various microbial phyla in the biofilm communities. Although only a small proportion of OPPPs were detected, this demonstrates their ubiquitous presence and persistence within these systems. Furthermore, functional prediction of the biofilm communities in these environments revealed involvement in various metabolic pathways such as nitrogen metabolism, bacterial secretion pathways, as well as novel functionalities that are yet to be explored.

In summary, the role of biofilm communities and the presence of Legionella, as well as other current and emerging OPPPs in premise plumbing systems is complex yet fascinating, with a huge interplay of various biological, chemical and physical factors. An improved understanding would subsequently aid in developing effective control strategies of OPPPs like Legionella for public health management. By reviewing various research studies published by others in the field, from the past and present in this blog post, I hope it can also become a bit of inspiration to formulate your own questions regardless of whether they are big or small, that may contribute to the field of knowledge. It certainly is as Sir Isaac Newton states: “If I have seen further, it is by standing on the shoulders of giants”.

Finally, still in the theme of microbiology, I would like to recommend an interesting review paper from Howard et al. (2020) that reviews the role of water, sanitation and hygiene (WaSH) in the context of present COVID-19 pandemic, as well as preparedness strategies to combat future pandemics as a result of emerging or re-emergent pathogens.

I hope this has been an enjoyable read and I hope to get the chance to meet you in a conference or workshop in the future, or alternatively, feel free to reach out.

In the meantime, please take care!

Casey Huang.

PhD Candidate

Advanced Water Management Centre, The University of Queensland.

kuantzu.huang [at] uqconnect.edu.au

List of references:

De Sotto, R., Tang, R. and Bae, S.  2020.  Biofilms in premise plumbing systems as a double-edged sword: microbial community composition and functional profiling of biofilms in a tropical region. J Water Health 18(2), 172-185.

Dietersdorfer, E., Kirschner, A., Schrammel, B., Ohradanova-Repic, A., Stockinger, H., Sommer, R., Walochnik, J. and Cervero-Aragó, S.  2018.  Starved viable but non-culturable (VBNC) Legionella strains can infect and replicate in amoebae and human macrophages. Water Res 141, 428-438.

Howard, G., Bartram, J., Brocklehurst, C., Colford, J.M., Jr, Costa, F., Cunliffe, D., Dreibelbis, R., Eisenberg, J.N.S., Evans, B., Girones, R., Hrudey, S., Willetts, J. and Wright, C.Y.  2020.  COVID-19: urgent actions, critical reflections and future relevance of ‘WaSH’: lessons for the current and future pandemics. Journal of Water and Health.

Wang, H., Bedard, E., Prevost, M., Camper, A.K., Hill, V.R. and Pruden, A.  2017.  Methodological approaches for monitoring opportunistic pathogens in premise plumbing: A review. Water Res 117, 68-86.


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