EU Drinking Water Directive reference methods for enumeration of total coliforms and Escherichia coli compared with alternative methods
F M Schets1, P J Nobel, S Strating
1National Institute for Public Health and the Environment (RIVM), Microbiological Laboratory for Health Protection, Bilthoven, The Netherlands. Ciska.Schets@rivm.nl
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.
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