A for Amoebae and Algae, B for Bacteria:
Rapid and sensitive detection of pathogenic microbes in the aquatic environment

n° 388 - December 2000


Researchers at the Oceanographic Observatory ("Observatoire océanologique biologique"*) in Banyuls-sur-Mer, working in collaboration with industry partners Chemunex**, EDF, and Indicia Diagnostic have developed a technique to detect pathogenic amoebae in waters. This method will subsequently be applied to the real time monitoring of toxic algae in seawater. It should soon replace traditional diagnosis methods, which are based on microbial cultures.

Rapid and sensitive detection of toxic algae is a major health concern due to food poisoning caused by contaminated shellfish. Currently, two to three days are required to diagnose the presence of pathogenic micro-organisms in the water. Direct detection methods such as epifluorescence microscopy or flow cytometry are faster, but sensitivity is too low.

A new protocol for detecting the amoeba Naegleria fowleri based on immunofluorescence, which is capable of detecting one amoeba in 10 milliliters of water, has been used to monitor the cooling water of the Civaux nuclear power station and revealed the absence of amoeba in these waters during summer 2000. An improved method exploiting magnetic separation is under development to analyze larger volumes of water.

Certain toxic algae such as Alexandrium minutum, Pseudo-nitzschia multiseries, and Dinophysis spp. are routinely monitored in coastal waters, but are detected only with difficulty at low sensitivity. A European program for their detection by solid-phase cytometry is underway.

Previous work has shown that it is possible to diagnose the viability of bacteria in minutes based on their metabolic activity and membrane integrity using fluorescent probes. The combination of this viability test and the specific detection of micro-organisms such as amoebae, algae and bacteria should enable the identity and viability of pathogenic microbes to be determined rapidly.

* CNRS-University Paris 6.

** http://www.chemunex.com.

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