Evaluation of an Inexpensive Growth Medium for Direct Detection of Escherichia coli in Temperate and Sub-Tropical Waters

Abstract

The cost and complexity of traditional methods for the detection of faecal indicator bacteria, including E. coli, hinder widespread monitoring of drinking water quality, especially in low-income countries and outside controlled laboratory settings. In these settings the problem is exacerbated by the lack of inexpensive media for the detection of E. coli in drinking water. We developed a new low-cost growth medium, aquatest (AT), and validated its use for the direct detection of E. coli in temperate and sub-tropical drinking waters using IDEXX Quanti-Tray®. AT was compared with IDEXX Colilert-18® and either EC-MUG or MLSB for detecting low levels of E. coli from water samples from temperate (n = 140; Bristol, UK) and subtropical regions (n = 50, Pretoria/Tshwane, South Africa). Confirmatory testing (n = 418 and 588, respectively) and the comparison of quantitative results were used to assess performance. Sensitivity of AT was higher than Colilert-18® for water samples in the UK [98.0% vs. 86.9%; p<0.0001] and South Africa [99.5% vs. 93.2%; p = 0.0030]. There was no significant difference in specificity, which was high for both media (>95% in both settings). Quantitative results were comparable and within expected limits. AT is reliable and accurate for the detection of E. coli in temperate and subtropical drinking water. The composition of the new medium is reported herein and can be used freely.

Evaluation of the novel substrate RUG™ for the detection ofEscherichia coliin water from temperate (Zurich, Switzerland) and tropical (Bushenyi, Uganda) field sites

“…False positive results of the test method can lead to unnecessary corrective actions and wasting of resources. 26 For AT-RUG, confirmation testing produced a false-positive rate of 6% during laboratory testing in Switzerland. This is in the range of reported false-positive rates for C-18 between 1 and 8%, [27][28][29] but lower than the reported rate for C-18 of 36.4% in tropical waters.…”

“…The US EPA guideline for evaluating new drinking water test methods recommends the assessment of E. coli detection media with very low contamination levels. 3 According to Bain et al 2015, 26 the assessment for the comparability of the MPN methods is more appropriate at higher contamination levels. This highlights the need for further investigation including natural water samples with low E. coli concentration to test whether AT-RUG with the Quanti-Tray®/ Legiolert system is capable of reliable E. coli quantification at low concentrations.…”

Development and field testing of low‐cost, quantal microbial assays with volunteer reporting as scalable means of drinking water safety estimation

“…; Bain et al . ), though at potentially greater cost. Given the potential for co‐detection of Klebsiella spp.…”

“…This LCPA as tested used mTec broth because it was locally available, inexpensive compared with alternatives, and detected E. coli reliably in laboratory testing both at standard incubation temperatures and at ambient temperatures (Table S1). While it compared well to the standard method, there are other chromogenic E. coli media available that have different specificity and sensitivity and may yield closer agreement with standard E. coli testing (Magro et al 2014;Bain et al 2015), though at potentially greater cost. Given the potential for co-detection of Klebsiella spp.…”

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

“…The AT presence-absence E. coli test was developed and piloted as part of a behavior-change randomized controlled trial (RCT) in rural India 1 . The semi-quantitative test uses the open-source Aquatest (AT) broth medium 22 with a resorufin methyl ester chromogen 23 (Biosynth AG, Switzerland) and subsequent incubation. Briefly, water samples are measured to 10 and 100 ml volumes using single-use volumetric cylinders containing premeasured AT medium.…”