Microplates: A Key Tool for Research and Enumeration of E. coli and Enterococci in Water

The most used indicators to assess contamination in water are Escherichia coli and intestinal enterococci. Today, the use of microplates has become the standard method of choice for analyzing seawater, freshwater, surface water, and wastewater, offering a reliable and standardized approach tailored to the needs of laboratories.

Why test  E. coli and enterococci in water?

E. coli and enterococci are indicators of pollution. Their presence in water intended for human consumption, bathing, or recreational use indicates a potential health risk, particularly the presence of pathogenic microorganisms.

• E. coli is an indicator of recent fecal contamination.
• Intestinal enterococci are more resistant in the environment and a good marker of persistent pollution, especially in bathing waters.

European and international regulations therefore impose standards to ensure the microbiological quality of water, such as:

• ISO 9308-1: Enumeration of E. coli and coliforms by membrane filtration for waters with low bacterial content
• ISO 9308-3: Detection and enumeration of Escherichia coli and coliform bacteria using the Most Probable Number (MPN) method in surface and wastewater
• ISO 7899-1: Detection and enumeration of intestinal enterococci by membrane filtration, with an equivalent Most Probable Number method for surface and wastewater

The principle of microplates in water analysis

Microplates are multi-well supports (generally 96 wells) that allow microbiological analysis to be carried out in a miniaturized and standardized manner. Applied to water microbiology, they rely on the Most Probable Number (MPN) principle combined with specific enzymatic reactions.

Each well contains a dehydrated culture medium which, after addition of the water sample and incubation, allows the growth of targeted bacteria and their identification through a chromogenic or fluorescent substrate.

This approach offers several advantages:

• time and space savings in the laboratory;
• easy reading and automated calculation;
• reduced handling and cross-contamination risks.

MUG/EC Microplate – Detection of E. coli

The MUG/EC microplate is dedicated to the detection and enumeration of E. coli according to the ISO 9308-3 method. This method has been developed for analysis of various types of water, including swimming and beach water in salt and fresh water, surface (still) water and post-treatment water.

It is based on the detection of β-glucuronidase activity, an enzyme characteristic of most E. coli strains.

Positive wells produce blue fluorescence under UV light after incubation for 48 hours at 44 ± 1°C.

This microplate provides a reliable solution for routine analyses and regulatory water quality controls.

MUD/SF Microplate – Detection of intestinal enterococci

The MUD/SF microplate is designed for the detection of intestinal enterococci according to the NF EN ISO 7899-1 method.

This method has also been developed in the analysis of various types of water, notably swimming and beach water in salt and fresh water, surface (still) water and post-treatment water.

Positive wells produce blue fluorescence under UV light after a minimum incubation period of 36 hours at 44 ± 1°C.

The microplate technique using MUD has been recognized as more specific, more accurate, more precise, and faster than previously used methods. It represents a significant improvement over conventional techniques for enterococci, which, among indicator microorganisms of fecal contamination, are of particular interest.

Conclusion

The use of microplates for detecting E. coli and enterococci is now a efficient solution that complies with current standards. Combining reliability, ease of use, and result standardization, they perfectly meet the requirements of water analysis laboratories.