\u201cEvery cell counts\u201d\u2014experiences with flow cytometry for Austrian drinking water supply

Abstract

The last decades have seen extensive scientific and technological improvements in many fields of microbiology and molecular biology. Correspondingly, flow cytometry—a rapid, precise and straightforward method for cultivation-independent detection of cells in liquids—has been a major topic in aquatic microbiology and drinking water analysis. Flow cytometry provides information at the single-cell level, including total cell counts, size measurements, nucleic acid content and bacterial viability and activity. While regulatory requirements for water testing rely on cultivation-based methods, flow cytometry can be considered a powerful tool to complement standard procedures.This article provides insights into the methodology and applicability of flow cytometry in the field of microbiological drinking water analysis and presents an overview on several case studies that cover a broad range of different objectives. The later are comprised of a study on flow cytometric characterization of Austrian drinking water resources, of an example for advanced data analysis methods of flow cytometric data, of a study on monitoring microbial regrowth within the distribution network, of an exemplary case of the application of online flow cytometry for high-frequency monitoring and of an introduction to the combination of flow cytometry and sequencing information.Finally, it is argued that due to the high microbiological variability of different water resources, unusual changes of flow cytometric parameters, rather than specific limits, could act as an indicator for further investigation. In this way flow cytometry can provide a good basis for risk assessments in water safety plans. The application of flow cytometry still remains utility-specific and a huge need for standardization of data analysis and interpretation exists in order to achieve a better cooperation of water utilities.