Interview: how flow cytometry is transforming the water industry

Flow cytometry has long been a staple in medical research and diagnostics, but its revolutionary impact on the water industry is only beginning to be realised. Professor emeritus Dr Thomas Egli, a microbiology expert and scientific consultant to bNovate, shares his journey and insights into how this technology is changing the microbiological drinking water analysis landscape.

Discovering potential in drinking water applications

Prof. Egli’s journey with flow cytometry began almost 20 years ago. His work at Eawag, the Swiss Federal Institute of Aquatic Science and Technology, focused on microbial activity, growth and biodegradation of pollutants in low-nutrient environments. In the early 2000s, while working with an OECD/WHO expert group on microbiological water analysis, he saw the potential of flow cytometry for drinking water applications.

“At that time, there was much enthusiasm for molecular detection methods which promised broad and fast pathogen screening on chips,” Prof. Egli recalls. “Flow cytometry was also considered as a potential rapid method, but thought too difficult, expensive and insensitive. However, hard- and software improvements in the late 1990s made detecting small microbial cells possible with the off-the-shelf flow cytometers.”

The birth of a new methodology

In 2003, Prof. Egli took charge of the drinking water microbiology group at Eawag. With support from his director, he invested in the first flow cytometer, a bulky and costly machine that proved invaluable. “We adapted methods for counting microbial cells and determining their metabolic activities in drinking water,” he explains. Collaborating with Zurich Water Works, they tested and applied these methods in practice, leading to a deeper understanding of microbial abundance and activity across the various drinking water production processes and distribution. 

Their pioneering work earned them the Mühlheim Water Award in 2010 for successfully transitioning flow cytometry from the lab to practical applications. 

Then bNovate entered the scene

In 2011, Peter Ryser, co-founder of bNovate, approached Prof. Egli after hearing about his work at Eawag. A year later, Ryser and Simon Kuenzi (bNovate’s other co-founder) were developing BactoSense, an automated, portable online flow cytometer for drinking water monitoring. “They invited me to join them as a microbiology scientific consultant, marking the start of our long-standing collaboration,” says Prof. Egli.

Flow cytometry impact on the water industry

Flow cytometry addresses two crucial questions in microbiological drinking water analysis: true microbial abundance and analytical speed. The established cultivation-dependent heterotrophic plate counting (HPC) method notoriously underestimates microbial presence by one or more orders of magnitude (a deficiency that has been criticised for the last 50 years). Flow cytometry total cell count (FCM-TCC), which uses fluorescent DNA-binding dyes to detect over 99% of microbial cells, provides a much more accurate picture in 20 minutes instead of three or more days as needed with HPC. “Flow cytometry, especially total cell counting (FCM-TCC), reveals the real number of microbial cells, challenging the long-held belief of virtually sterile drinking water,” Prof. Egli notes. 

FCM-TCC is now gaining acceptance as an alternative to the traditional, established HPC method. Furthermore, with the BactoSense instrument, water professionals have, for the first time, a method at hand that allows continuous online monitoring of a fundamental microbiological parameter from source through production to the tap.

Future of microbiological water monitoring

Prof. Egli sees a bright future for flow cytometry in the water industry. “I expect FCM-TCC and membrane integrity intact cell counting (ICC) to become routine methods for microbiological water analysis,” he predicts. He also anticipates the development of additional activity parameters to complement these basic methods, enhancing our ability to monitor water quality. 

Prof. Egli highlights the potential for simple instruments relying on cellular autofluorescence for surface water monitoring. “With increasing water temperatures, reservoirs and lakes used as sources of raw water for drinking water production are more vulnerable to pollution by cyanobacteria and algae,” he explains. 

Moreover, he foresees significant advancements in the automated detection of hygiene indicator organisms and specific pathogens using enzyme activity-based methods or immunomagnetic fishing. “The challenges lie in achieving more speed, better specificity, and sensitivity,” he notes. Here, he expects offline procedures to be favoured and is cautious about the feasibility of routine online pathogen detection becoming widespread. “Exceptions may include the online detection of frequently occurring microbes such as E. coli and enterococci in surface and raw water, P. aeruginosa in the bottled water industry, or legionella and mycobacteria in cooling towers,” he adds. “Flow cytometry, including devices like BactoSense, may be among several methods used for fast and economical quantification of target organisms,” he says.  

Widespread adoption and new standards

Prof. Egli is confident in the widespread adoption of flow cytometry for water quality monitoring. “No other method can deliver such comprehensive microbiological information at such a low cost,” he asserts. He cites Switzerland’s successful implementation of FCM-TCC as a model, with other European countries beginning to follow suit. You can already see this endorsement in Switzerland by SVGW (already in 2012 by the Federal Office of Public Health, now available on the method platform of the SVGW), Austria and Germany. “I’m confident that an ISO-standard method will eventually be established, driven by bottom-up pressure and growing recognition of the benefits of flow cytometry.” 

In summary, flow cytometry is revolutionising the water industry by providing accurate, rapid analysis of microbial cells in drinking water. With continued advancements and broader adoption, it promises to become the new standard in microbiological water analysis.