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.