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. 2015 Oct 23;10(10):e0140997.
doi: 10.1371/journal.pone.0140997. eCollection 2015.

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

Robert E S Bain  1 , Claire Woodall  2 , John Elliott  3 , Benjamin F Arnold  4 , Rosalind Tung  5 , Robert Morley  6 , Martella du Preez  7 , Jamie K Bartram  8 , Anthony P Davis  2 , Stephen W Gundry  9 , Stephen Pedley  3
Affiliations

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

Robert E S Bain et al. PLoS One. .

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.

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Conflict of interest statement

Competing Interests: SWG was employed as Professor of Environmental Engineering by the University of Bristol whilst this research study took place. He acted as the Project Director and Principal Investigator for the Aquatest project. SWG is named as the sole inventor on European patent number 1960104 entitled: Apparatus for determining the presence of a contaminant in a sample of water or other fluid. Patents for this apparatus have been granted or are pending in a number of other countries. SWG and RB are named as coinventors on International Patent Application number PCT/GB2010/050728 entitled Apparatus for testing the quality of a fluid sample and SWG and RB are named inventors on an international patent application number PCT/GB2012/050452 of the same name. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. Although named as co-inventors in the patents cited, neither SWG nor RB derive any financial advantage therefrom. SWG retired from the University of Bristol in May 2014. He set up an R&D company, Brightwater Diagnostics Limited, which is in a start up phase and has not commenced trading. RT is a consultant that currently collaborates with CPI International, a manufacturer of water testing kits. None of the formulations of CPI’s water testing kits are the same as the Aquatest formulation.

Figures

Fig 1
Fig 1. Scatter plots of aquatest E. coli estimates versus Colilert-18®, EC-MUG and MLSB in temperate water samples.
Fig 2
Fig 2. Difference versus mean plots for aquatest E. coli estimates versus Colilert-18®, EC-MUG and MLSB in temperate water samples.
Fig 3
Fig 3. aquatest E. coli estimates versus Colilert-18® (A) scatter plot and (B) difference versus mean in sub-tropical water samples.
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