A novel, reliable and rapid method for detecting living bacteria

One of the major challenges in terms of microbiological quality control and public health is to be able to count and identify, both quickly and simultaneously, the bacteria living in an environment.

An innovative and reliable method has recently been developed by a team from the Laboratoire de Chimie Bactérienne of the Institut de Microbiologie de la Méditerranée (CNRS/Aix-Marseille Université) and the Laboratoire de Glycochimie Moléculaire et Macromoléculaire of the Institut de Chimie Moléculaire et des Matériaux d'Orsay (CNRS/Université Paris-Sud).

This work has been published in Angewandte Chemie on 9 February 2012. A patent covering this method has also been filed.
 
The technique developed by the team makes it possible to detect living Gram-negative type bacteria, which include pathogens such as Escherichia coli, Salmonella typhimurium and Legionella pneumophila.

To do so, the bacteria are placed in contact with KDO, a sugar that bacteria use to synthesise a specific polysaccharide of their cell membrane.

However this sugar is modified beforehand through the introduction of an azide function (made up of three atoms of nitrogen). Deceived, the bacteria incorporate the artificial sugar in their membrane. Then, thanks to a fluorescent molecule that attaches exclusively to the azide group, it is possible to identify and count living Gram-negative bacteria, the only ones to have assimilated the modified KDO.
 
The importance of these results stems from the fact that there is no rapid technique that allows living bacteria of interest to be simultaneously detected and counted.

Furthermore, current methods used to count living bacteria are not entirely satisfactory: those requiring to put bacteria in a culture medium are slow (up to several weeks), whereas rapid methods can give false negatives or positives. This new technique combines reliability with rapidity in the detection of living bacteria. Consequently, it could quickly become an indispensable tool in terms of microbiological quality control and public health.
 
Experiments conducted by the researchers on Gram-negative type bacteria validate this method. In the future, the use of a specific sugar of each bacterium of interest could allow the detection of a very wide range of living pathogenic bacteria.