Synthesis and application of resorufin ß-D-glucuronide, a low-cost chromogenic substrate for detecting Escherichia coli in drinking water.

The development of low-cost tests for Escherichia coli is hampered by the expense and limited choice of enzyme substrates. Most chromogenic substrates are required in costly amounts, while fluorogenic substrates require an additional apparatus (e.g., an ultraviolet lamp) to be detected. Herein, we propose an alternative chromogenic substrate, resorufin ß-d-glucuronide (REG), which is exceptionally sensitive and may be employed in very small amounts. We show that REG can be produced similarly to other simple glucuronides and should therefore be no more expensive. The compound is used by both healthy and injured E. coli, resulting in a pronounced color change from orange to a bright pink. Because the released dye (resorufin) has a high extinction coefficient, substantially lower amounts are needed than for commercially available substrates. The potential of this substrate is demonstrated by a presence/absence test requiring just 0.1 mg of REG/100 mL of water sample, one hundredth of the quantity needed for common chromogenic substrates, with an estimated bulk cost of ≤0.1 U.S. cents/test. REG shows promise as a chromogenic substrate for E. coli detection and should be considered in the development of new water tests, especially for low-income settings.

Broader incubation temperature tolerances for microbial drinking water testing with enzyme substrate tests.

Microbiological testing is an integral part of measures to ensure safe drinking water. However, testing can be restricted in low-resource settings by the requirement for specialized laboratory facilities and testing procedures. Precisely controlled incubation temperature is one example. The effect of varied incubation temperatures on the performance of two enzyme substrate tests for the detection of Escherichia coli and total coliforms has been examined. The aim was to determine whether these tests would provide consistent and comparable enumeration over a broader temperature range than currently specified. Recovery of chlorine-injured and wild type E. coli was examined over a range of non-standard incubation temperatures in comparison to 37 °C ± 1. Colilert(®) and Aquatest, a new E. coli-specific detection medium, served as the two representative enzyme substrate media. Recovery of chlorine-injured E. coli in Colilert was not impaired within the range 33-39 °C; the equivalent range in Aquatest medium was 31-43 °C. Both these tests recovered E. coli without significant loss of performance over a wider range of temperatures than currently specified.

Disinfection of waterborne coliform bacteria using Luffa cylindrica fruit and seed extracts.

This study examined the potential of extracts of the plant Luffa cylindrica to act as disinfectants of drinking water. Aqueous extracts of the seeds and fruit of L. cylindrica were tested against total and faecal coliform bacteria in surface water by varying the extract doses and contact times. Inactivation of both faecal coliforms and total coliforms was highly variable and dose-dependent. The maximum coliform inactivation achieved in any trial was 86%. Fruit extracts were more successful at inactivating total coliforms than faecal coliforms. Seed extracts achieved higher coliform inactivation levels than fruit extracts generally. Overall, the antimicrobial potential of seeds and fruit from L. cylindrica was demonstrated; however the disinfection performance was less than would be required for these extracts to be considered reliable disinfectants for drinking water treatment.