Hydrologie : recherche actuelle

Total Colony Counts (TCC) By Flow Cytometry (FCM) Should Replace the Heterotrophic Plate Count (HPC) Test for Bacteriological Enumeration of Water - Some Recent Developments in Flow Cytometry: A Review

Abstract

Thavrin Manickum

We currently use the gold standard HPC test method for bacterial enumeration of our raw, drinking and waste water; analysis times are relatively long: 1-3 d, as per the
international standard reference method. Our tests are accredited to ISO/IEC 17025 requirements. The literature has indicated international use of the current HPC
method for monitoring routine microbiological quality of drinking water; current tests for pathogen monitoring have poor sensitivity, accuracy and long analysis times, in
general. The aim of this current review is to: Consider shortfalls of the HPC method, Discuss alternative methods for bacterial enumeration, Discuss features and
applications of the automated -sample preparation flow cytometer, the BactoSense model, Highlight advantages of flow cytometry, which makes this technique the choice
for the bacteriological enumeration in water, and Propose options for standardization of flow cytometry TCC test methods.
Findings indicate that HPC is very inaccurate (~ -99% bias), and time-consuming (1-3 d), compared to flow cytometry (~ 99% accurate; ± 15-20 min analysis time). The
evidence confirms a strong preference for the use of flow cytometry for Total Cell Counts/mL; the BactoSense is one viable instrument due to its automated sample
preparation, speed of analysis, accuracy and precision. There was a significant gap regarding the standardization of current flow cytometry test methods. Options for
standardization are ISO/IEC 17025 accreditation, the US EPA, ASTM, AOAC, and Standard Methods. Some key method validation parameters are: accuracy, bias,
precision, specificity, LOD, LOQ, linearity, and the Uncertainty of measurement. The review has highlighted the potential of flow cytometry for the screening of Corona
virus SARS-CoV-2 for COVID-19. The BactoSense FCM appears to be a viable option for bacterial enumeration, as a TCC/mL measure, for drinking water, due to its
sample preparation automation, speed of analysis, accuracy and precision. The current, and new, FCM test methods should be validated, standardized, or accredited for
adoption for bacterial enumeration of water. Flow cytometry is the preferred test method for bacterial enumeration of water - it should replace the HPC method.