Novel methods for global water safety monitoring: comparative analysis of low-cost, field-ready E. coli assays

Abstract

Current microbiological water safety testing methods are not feasible in many settings because of laboratory, cost, and other constraints, particularly in low-income countries where water quality monitoring is most needed to protect public health. We evaluated two promising E. coli methods that may have potential in at-scale global water quality monitoring: a modified membrane filtration test followed by incubation on pre-prepared plates with dehydrated culture medium (CompactDry TM), and 10 and 100 ml presence-absence tests using the open-source Aquatest medium (AT). We compared results to membrane filtration followed by incubation on MI agar as the standard test. We tested 315 samples in triplicate of drinking water in Bangalore, India, where E. coli counts by the standard method ranged from non-detect in 100 ml samples to TNTC (>200). Results suggest high sensitivity and specificity for E. coli detection of candidate tests compared with the standard method: sensitivity and specificity of the 100 ml AT test was 97% and 96% when incubated for 24 h at standard temperature and 97% and 97% when incubated 48 h at ambient temperatures (mean: 27°C). Sensitivity and specificity of the CompactDry TM test was >99 and 97% when incubated for 24 h at standard temperature and >99 and 97% when incubated 48 h at ambient temperatures. Good agreement between these candidate tests compared with the reference method suggests they are suitable for E. coli monitoring to indicate water safety.

Monitoring Drinking Water Quality in Nationally Representative Household Surveys in Low- and Middle-Income Countries: Cross-Sectional Analysis of 27 Multiple Indicator Cluster Surveys 2014–2020

“…2012 ). In the MICS, an adapted membrane filtration process has been used, yielding reliable quantitative results ( Brown et al. 2020 ).…”

Microbial Indicators of Fecal Pollution: Recent Progress and Challenges in Assessing Water Quality

“…The compounding complexity required for reliable results suggests that qPCR in its current form may be unsuitable for routine monitoring purposes except in particularly well-resourced laboratories that regularly process sufficient sample numbers to warrant the equipment, properly maintain assay materials, and ensure sustained institutional experience. By contrast, culture-based FIB detection has grown increasingly accessible following recent efforts to develop low-cost field tests that can be performed with minimal equipment at ambient temperatures [ 125 , 169 , 170 ]. While still requiring substantial resources and expertise, dPCR requires fewer controls and precise reference materials than qPCR because it is robust to matrix interference and offers absolute quantification, features which may position dPCR to be increasingly adopted for general use [ 171 ].…”

Monitoring drinking water quality in nationally representative household surveys: cross-sectional analysis of 20 Multiple Indicator Cluster Surveys 2014-2019

“…There are several water quality tests that could potentially be integrated in household surveys (Bain et al 2012). In the approach used in MICS an adapted membrane filtration process has been used, yielding reliable quantitative results (Brown et al 2020). The costs are approximately $2.5 per test using the new "E. coli only” Compact Dry plates and $1500 per team for hardware (mainly the filtration equipment) but these are expected to reduce over time.…”

“…northern Nigeria, Afghanistan). Ambient temperature and phase change incubators are both potential solutions (Brown et al 2011) and CompactDry™ plates have been shown to perform favourably when compared to reference methods when incubated at ambient temperature in Bangalore, India (Brown et al 2020).…”