Methods for microbiological quality assessment in drinking water: a comparative study

Abstract

The present study aimed to compare several methods for quantifying and discriminating between the different physiological states of a bacterial population present in drinking water. Flow cytometry (FCM), solid-phase cytometry (SPC), epifluorescence microscopy (MSP) and culture method performances were assessed by comparing the results obtained for different water samples. These samples, including chlorinated and non-chlorinated water, were collected in a drinking water treatment plant. Total bacteria were quantified by using SYBR Green II (for FCM) and 4',6'-diamino-2-phenylindole (DAPI) (for MSP), viable and non-viable bacteria were distinguished by using SYBR Green II and propidium iodide dual staining (for FCM), and active cells were distinguished by using CTC (for MSP) and Chemchrome V6 (for FCM and SPC). In our conditions, counts using microscopy and FCM were significantly correlated regarding total bacteria and active cells. Conversely, counts were not significantly similar using solid-phase and FCM for active bacteria. Moreover, the R2A medium showed that bacterial culturability could be recovered after chlorination. This study highlights that FCM appears to be a useful and powerful technique for drinking water production monitoring.

Laboratory-Scale Simulation and Real-Time Tracking of a Microbial Contamination Event and Subsequent Shock-Chlorination in Drinking Water

“…Potential further investigations include real-time tracking of various different disinfection strategies on bacteria (e.g., heat, surfactants, sunlight, heavy metals, membrane targeting antibiotics) ( Suller and Lloyd, 1999 ; Berney et al, 2006 ; Bigoni et al, 2014 ). The differentiation between TCC and ICC is a strength of FCM ( Helmi et al, 2015 ; Van Nevel et al, 2017b ) and can easily be extended to other viability/activity dyes to enable deeper insights into disinfection processes ( Nebe-von-Caron et al, 2000 ; Tracy et al, 2010 ). While manual and automated ATP-assays can also deliver information on viability ( Vang et al, 2014 ; Nescerecka et al, 2016 ), continuous ATP measurements are currently not possible.…”

“…This is only feasible through full automation of in situ sampling, sample preparation, and measurements. Rapid microbial detection methods that are suitable to assess both contamination and disinfection include for example ATP assays ( Vang et al, 2014 ; Nescerecka et al, 2016 ) and flow cytometry (FCM) using viability staining protocols ( Hammes et al, 2012 ; Helmi et al, 2015 ). With respect to FCM, examples of automated, in situ monitoring of microbial dynamics were previously shown for total cell concentration (TCC) and discrete sampling (15-min resolution) ( Brognaux et al, 2013 ; Besmer et al, 2014 , 2016 ; Besmer and Hammes, 2016 ) and for enzymatic reactions as well as GFP-labeled bacteria and continuous sampling (1-min resolution) ( Nolan and Sklar, 1998 ; Broger et al, 2011 ; Arnoldini et al, 2013 ).…”

Flow cytometric bacterial cell counts challenge conventional heterotrophic plate counts for routine microbiological drinking water monitoring

“…Several studies have examined the fraction of intact, active and respiring bacteria in drinking water. In nonchlorinated drinking water, -70 % of the total cells detected with FCM after SYBR Green I staining were demonstrated to be active (esterase activity measured with CFDA staining and FCM) and 70 -% of the cells had intact membranes (measured with propidium iodide staining and FCM) (Berney et al, 2008;Helmi et al, 2014a). When chlorine residual was lost in a chlorinated system, samples contained 50 -60 % cells with intact membranes (Kahlisch et al, 2012).…”

“…A large number of viability dyes are commercially available and have been tested in various research settings (Berney et al, 2008;Helmi et al, 2014a). The future challenge in this field is to select dyes based on (i) the mechanism of cellular death that is evaluated (e.g., chlorination permeabilising cells) and (ii) the mechanistic action of the dye (e.g., penetrating permeabilised cells).…”

Understanding wastewater treatment mechanisms: a review on detection, removal, and purification efficiencies of faecal bacteria indicators across constructed wetlands

“…To address some of these shortcomings of FC, a solid phase laser scanning analyzer that has higher detection at low concentrations is being used as an alternative (Deere et al, 2002). Despite it having higher detection capabilities, it is expensive and complex to operate (Helmi et al, 2015). Cell Sorting Flow Cytometer (CSFC) has also been incorporated in CW studies (Doherty et al, 2010;Guez-Barber et al, 2012).…”