Thursday, March 20, 2014

(Bio-) Chemists Without Borders: Help Aqueous Solutions Hack Field E. coli Testing!

Biochemists and microbiologists: Aqueous Solutions has a mission for you.

By Josh Kearns
I recently visited two village training centers deep in the wilds of Tenasserim district (Thailand-Burma border region), where colleagues and I conducted follow-up inspections on water treatment systems installed by local trainees during recent months. (Check out our Facebook page for photos from the trip.)

On this trip and the other routine visits we make to project sites, in addition to troubleshooting, refurbishment, and data collection to supplement our research objectives, we perform microbiological testing to verify drinking water safety. For this task we have been using 3M Petrifilms, which indicate total coliforms as well as E.coli in a 1 mL water sample.

Local trainees conducting E.coli testing.

Over the years, Petrifilms have proved indispensible for validating our treatment system designs, as they are the most practical and economical (about US$2 per test) test for microbiological water quality that we have yet come across.

Naw Gay Pho giving instruction on interpretation of the microbial tests.

Their main drawback, though, is the 1 mL sample volume. The international World Health Organization (WHO) standard for water quality includes the criteria for E.coli of less than one colony-forming unit (CFU) per 100 mL. With a 1 mL sample volume, this standard is thus two orders of magnitude below the detection level of the Petrifilm test.

However, a new field-oriented commercial E.coli test kit was recently brought to our attention. This method makes use of a 100 mL sample volume, and a simplified approach to most-probable-number (MPN) analysis – allowing for better precision and achieving a lower, WHO-approved detection level.

Unfortunately, at over US$10 per test, this particular E.coli testing system is priced well out of the range of affordability for small, grassroots NGOs like Aqueous Solutions and our community based partners. Furthermore, these test kits are rather bulky, containing a lot of single-use plastic ware. This would make it cumbersome, if not impossible, for example, to hike distances in remote, rugged terrain with enough supplies for testing several water sources and treatment systems. Moreover, the single-use plastic ware presents a safe and environmentally responsible disposal challenge. (Where we work, it’s not a matter of phoning up the local EH&S to come by and properly dispose of our bio-waste!)

We have, however, devised a “hack,” that will allow us to use the basis of this commercial method but at greatly reduced cost, and with less bulky and reusable equipment.

The hack is nearly complete, but we lack one key ingredient: 5-Bromo-4-chloro-3-indolyl β-D-glucuronide, also known as “X-Gluc.” X-Gluc is a chromogenic indicator that produces a blue color in the presence of E.coli.

So, Biochemists and Microbiologists Without Borders, your mission, should you choose to accept it, is to help Aqueous Solutions identify a convenient and economical source of X-Gluc.

The ideal form would be a tablet pre-dosed for 100 mL sample volume. Sigma-Aldrich sells tablets, but they are quite expensive. We contacted the company selling the MPN test kits described above about purchasing their E.coli media pellets but they will not sell them separately from the test kits. And since the media pellets are proprietary, they will not provide any information about how to acquire them directly or derive our own.

(As an editorial aside, this is an example of how intellectual property can inhibit rather than promote innovation, as is commonly claimed. Our goal is not to undermine the market for this company’s product, but to build on the extant research and development to adapt the system for other scenarios where it is currently infeasible – and therefore there currently is no market. Making knowledge artificially scarce by keeping the E.coli media formulation proprietary is obviously unhelpful from the perspective of the many communities who could benefit from water testing…)

Anyway, that’s our pitch. Any leads for how we can secure a supply of X-Gluc in a cost effective manner would be much appreciated! We are really excited about this hack and the potential it represents to increase the sensitivity and robustness of our water system validation field protocol!

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  1. Thanks for all your great posts, Josh. Have you approached Sigma-Aldrich, et al., and asked them to sponsor your work by donating the X-Gluc? I have been surprised by the generosity of many companies. Peace, Bego

  2. Good thought, Bego - I will try that... JK