Detection of viable pathogenic bacteria from water samples by PCR

The Polymerase chain reaction (PCR) is a molecular technique which can be used for identify specific bacterial strains within a mixed population. A detection method has been developed for strict and opportunistic pathogenic bacteria (Salmonella, enterohemorragic Escherichia coli and Aeromonas hydrophila) in raw and treated water. This method is composed of a bacterial DNA purification step followed by PCR detection. Compared to the traditional culture techniques, this method has an enhanced specificity and sensitivity. Furthermore, the simple and rapid protocol of the proposed technique provides results at a fraction of the time required by the traditional culture techniques (24 hours compared with 2 to 6 days). However, unlike the culture methods, detection by PCR does not provide information related to the viability of the bacteria since the detected bacteria can be viable and cultivable, viable but non-cultivable, or dead. The viability concept is very important for interpreting the detection of pathogenic bacteria in relation to public health issues. To overcome this limitation, an indirect approach has been developed for assessing the viability of PCR detected bacteria from water samples. This method is based on the analysis of each sample before and after a 20hour culture step in a non selective medium: an increase in the PCR response after cultivation indicates the occurrence of bacterial multiplication and thus demonstrates the viability of the detected bacteria. This new protocol allows the simultaneous detection of several viable cultivable pathogenic bacteria by PCR from water samples.