Flow Cytometry for Rapid Microbiological Analysis of Drinking Water: From Science to Practice, an Unfinished Story
Thomas Egli and Stefan Kötzsch
from: Flow Cytometry in Microbiology: Technology and Applications (Edited by: Martin G. Wilkinson). Caister Academic Press, U.K. (2015) Pages: 175-216.
For many years routine microbiological analysis of drinking water has been dominated by plating methods. Established by Koch more than a century ago, the world-wide standards include both indicator organisms for faecal contamination as hygiene parameters (Escherichia coli, coliforms, enterococci), and the "heterotrophic plate count" (HPC) as a general parameter of microbiological water quality. These methods are slow, requiring 1-10 days before data become available. In particular, the HPC has been criticized over the past 30 years as underestimating the real number of microbial cells by two or three orders of magnitude. Flow cytometry offers a range of options to detect cells quickly, and we have recently explored the potential of a number of FCM-based methods for rapid (< 1h) microbiological analysis of drinking and surface waters. These include total cell counting (TCC), the ratio of small/big cells (LNA:HNA-ratio), community fingerprints, assessing cell viability and physiological state (all in 15min), or detection and quantification of selected pathogens (in < 2h). Determination of TCC and the LNA:HNA-ratio are now officially accepted and recommended parameters for freshwater analysis in Switzerland. Determination of the TCC by flow cytometry is already routinely used by a number of Swiss and Dutch drinking-water suppliers. FCM has been proven to allow fast and realistic assessment of water treatment processes and rapid quantification of microbial regrowth and bio(in)stability in drinking-water distribution networks and in public and private buildings. In addition, online monitoring of TCC has already been reported and will be commercially available shortly. The potential for applications of FCM-based methods in the field of drinking-water analysis is still far from being fully exploited read more ...