title: Flow cytometric bacterial cell counts challenge conventional heterotrophic plate counts for routine microbiological drinking water monitoring.
abstract: Drinking water utilities and researchers continue to rely on the century-old heterotrophic plate counts (HPC) method for routine assessment of general microbiological water quality. Bacterial cell counting with flow cytometry (FCM) is one of a number of alternative methods that challenge this status quo and provide an opportunity for improved water quality monitoring. After more than a decade of application in drinking water research, FCM methodology is optimised and established for routine application, supported by a considerable amount of data from multiple full-scale studies. Bacterial cell concentrations obtained by FCM enable quantification of the entire bacterial community instead of the minute fraction of cultivable bacteria detected with HPC (typically < 1% of all bacteria). FCM measurements are reproducible with relative standard deviations below 3% and can be available within 15 min of samples arriving in the laboratory. High throughput sample processing and complete automation are feasible and FCM analysis is arguably less expensive than HPC when measuring more than 15 water samples per day, depending on the laboratory and selected staining procedure(s). Moreover, many studies have shown FCM total (TCC) and intact (ICC) cell concentrations to be reliable and robust process variables, responsive to changes in the bacterial abundance and relevant for characterising and monitoring drinking water treatment and distribution systems. The purpose of this critical review is to initiate a constructive discussion on whether FCM could replace HPC in routine water quality monitoring. We argue that FCM provides a faster, more descriptive and more representative quantification of bacterial abundance in drinking water.
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000, Gent, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Van Nevel
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Koetzsch
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland; Department of Environmental Systems Science, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland.
authors.forename: C R
authors.initials: CR
authors.lastname: Proctor
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.
authors.forename: M D
authors.initials: MD
authors.lastname: Besmer
authors.affiliation: Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ, Delft, The Netherlands.
authors.forename: E I
authors.initials: EI
authors.lastname: Prest
authors.affiliation: Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ, Delft, The Netherlands; Wetsus, Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911 MA, Leeuwarden, The Netherlands; King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia.
authors.forename: J S
authors.initials: JS
authors.lastname: Vrouwenvelder
authors.affiliation: Het Waterlaboratorium, J.W. Lucasweg 2, 2031 BE, Haarlem, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Knezev
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000, Gent, Belgium.
authors.forename: N
authors.initials: N
authors.lastname: Boon
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland. Electronic address: frederik.hammes@eawag.ch.
authors.forename: F
authors.initials: F
authors.lastname: Hammes
mesh_terms: D001419:Bacteria; D002452:Cell Count; D015169:Colony Count, Microbial; D060766:Drinking Water / Q000382:microbiology*; D005434:Flow Cytometry; D014871:Water Microbiology; D060753:Water Quality; D014881:Water Supply
chemical_list: D060766:Drinking Water
keywords: Cultivation; Flow cytometry (FCM); Heterotrophic plate counts (HPC); Microbiological drinking water quality; Routine water monitoring