The European trial exercise on Escherichia coli detection in bathing waters

The microbiological quality of environmental water that can be used for bathing in the European Union (EU) is regulated by the Bathing Water Directive (BWD) 2006/7/EC based on parametric values established for intestinal enterococci and Escherichia coli (E. coli). Detection and enumeration of E. coli under the BWD relies on the culture-based reference methods, which would require 1-2 days to obtain results, a considerable long time for decision making by public authorities when contamination of bathing water occurs. BWD allows the use of alternative methods if the reliability of a selected method is at least equal to that of the standard method. The development of alternative methods requires evaluation in multiple laboratory trials according to ISO 16140-2:2016, which provides a standardised protocol for the validation of such methods against reference methods in foodstuffs and environmental samples. The present report describes the EU-wide trial exercise aimed at validating a molecular based method, the real-time polymerase chain reaction (PCR) for the detection of E. coli in bathing water. Compared to the culture-based methods, molecular techniques allow to reduce the time to results to a few hours. In particular, real-time PCR has the advantage of specifically and rapidly detect and quantify bacterial target genes.