EU Drinking Water Directive reference methods for enumeration of total coliforms and Escherichia coli compared with alternative methods.

AIMS The reference methods for enumeration of total coliforms and Escherichia coli as stated in the European Drinking Water Directive were compared with alternative methods. METHODS AND RESULTS Laboratories used the reference method on Lactose TTC agar (LTTC), the Colilert/18 system, Laurysulphate Agar (LSA), Chromocult Coliform Agar and the E. coli Direct Plating (DP) method. They enumerated more total coliforms on LTTC than on LSA. CONCLUSIONS LTTC is suitable for analysis of very clean water samples only, due to heavy background growth. Colilert/18 is a good alternative but it enumerates a broader group of total coliforms, resulting in higher counts. The DP method appeared to be the best choice for enumeration of E. coli because Colilert/18 produces lower counts and false-negative results. SIGNIFICANCE AND IMPACT OF THE STUDY This study shows the limitations of the EU reference method on LTTC due to lack of selectivity and suggests alternative methods for the enumeration of total coliforms and E. coli.