Enterolert-DW Is Now an ISO Standard for Enterococci Numeration
Testing for enterococci in drinking and recreational waters has become an essential safeguard for public health. These primarily intestinal bacteria serve as indicators of fecal contamination, and their presence can signal potential exposure to harmful pathogens. The European Union (EU) Drinking Water Directive requires one-to-one testing for enterococci alongside E. coli, underscoring their importance in assessing water safety.
The IDEXX Enterolert-DW test for enterococci recently reached a significant milestone with its publication as International Organization for Standardization (ISO) Standard 7899-3, which specifies the Most Probable Number (MPN) method for detecting and counting intestinal enterococci. This recognition validates Enterolert-DW as a globally accepted method for enumerating enterococci in both drinking and bathing water, providing water utilities and laboratories with an internationally recognized tool.
Below, we'll discuss how the test works, what organisms it detects, and the benefits it provides to water utilities and labs. We'll also highlight the performance characteristics of Enterolert-DW (ISO 7899-3) assessed according to ISO 13843 and discuss the implications of this new standard for global water safety.
How Does Entercocci Testing Help Regulators Monitor Water?
Enterolert-DW detects a broad range of intestinal Enterococcus species, including E. faecalis, E. faecium, E. hirae, E. gallinarum, E. casseliflavus, E. durans, and E. avium. These organisms are recognized worldwide as reliable indicators of fecal contamination, particularly in treated drinking water and bathing waters where rapid response is essential to safeguard public health.
By targeting this broad group of enterococci, Enterolert-DW enables utilities, public health laboratories, and regulators to effectively monitor water quality, consistent with international standards such as ISO and EU regulations, as well as with national standards such as AFNOR 'NF Validation' Certification and the U.K. Standing Committee of Analysts' "Blue Book" and Water Inspectorate.
Understanding the Methodology
Enterolert-DW employs Defined Substrate Technology (DST), which relies on a nutrient indicator to detect the presence of enterococci. The medium contains ortho-Nitrophenyl-β-D-glucoside in a blue background. When metabolized by enterococci, this substrate produces a distinct green color. Confirmation is not required.
To conduct the test:
- Pair DST reagent with the IDEXX Quanti-Tray or Quanti-Tray/2000 system, which allows quantification through the Most Probable Number (MPN) approach.
- Add the reagent to a 100 mL sample, seal it into the tray, and incubate.
- After 24 hours at 41°C, wells that contain enterococci turn green.
- Look up the number of positive wells on an MPN table to deliver a result.
This straightforward workflow uses the same IDEXX platform as Colilert-18 (ISO 9308-2), Pseudalert (ISO 16266-2), and Legiolert (ASTM D8429-21), allowing laboratories to adopt this method without changing their existing equipment or training protocols.
Rapid Results Enable Rapid Responses
One of the key advantages of the MPN method is the rapid turnaround time for tests. Results from the test are available in as little as 24 hours, with positive detections sometimes observable within this timeframe. Other benefits of this method include:
- Ease of use: The method requires less than one minute of hands-on time, thanks to the pre-measured, unit-dose format.
- Less chemical risks: No media preparation or toxic reagents are involved, reducing both workload and safety concerns.
- Fewer ambiguities: The green/blue color change eliminates subjective interpretation that can occur with traditional culture methods, ensuring greater consistency across labs.
- Rapid results: With results available within 24 hours, laboratories can quickly communicate results, enabling better protection of public health and safety.
For water utilities, public health and private laboratories, these efficiencies translate into faster decision-making, enhanced productivity, more reliable compliance monitoring, and reduced risk of error.
Rigorous Validation as a Foundation for Accuracy
The publication of Enterolert-DW as ISO 7899-3 reinforces Enterolert-DW's position as a trusted method for testing drinking water, as well as fresh and marine bathing waters, including samples with a large amount of suspended matter. The method underwent rigorous validation in accordance with ISO requirements was benchmarked against other established reference methods.
According to the ISO 13843 method performance validation study, Enterolert-DW achieved the following parameters:
- Sensitivity: 91.9%
- Specificity: 93.0%
- Selectivity: 42.1% (well above the ISO guidance threshold of >10%
- Efficiency: 91.7%
- Counting repeatability: 3.4%
- Counting reproducibility: 3.1%
- Method repeatability: 15.4%
- Method reproducibility: 17.5%-33.8%
When compared to ISO 7899-2, Enterolert-DW showed higher overall recovery rates, particularly in chlorinated samples. Against the Microbiology of Drinking Water (MoDW) 2012 Part 5 standard, results were statistically similar overall: higher in chlorinated waters and slightly lower in unchlorinated samples.
This combination of sensitivity, reproducibility, and robustness confirms Enterolert-DW's suitability for routine monitoring programs under international standards.
Meeting Global Standards To Keep Global Communities Safe
As water quality challenges continue to grow, new tools will help ensure that labs and utilities can meet regulatory requirements and protect global communities. With its ISO 7899-3 designation, Enterolert-DW joins a select group of microbiological methods that are recognized worldwide. For regulators, this allows harmonization across borders. For laboratories, it provides an easier path to compliance. And for communities, it means more reliable protection of public health in both drinking and bathing waters.
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