Equivalency testing of TTC Tergitol 7 agar (ISO 9308-1:2000) with five culture media for the detection of E. coli in water samples in Greece

摘要

In this study ten laboratories in Greece compared the performance of reference method TTCnTergitol 7 Agar (with the additional test of b-glucuronidase production) with five alternativenmethods, to detect E. coli in water, in line with European Water Directive recommendations.nThe samples were prepared by spiking drinking water with sewage effluent following a standardnprotocol. Chlorinated and non-chlorinated samples were used. The statistical analysis was basednon the mean relative difference of confirmed counts and was performed in line with ISO 17994.nThe results showed that in total, three of the alternative methods (Chromocult Coliform agar,nMembrane Lauryl Sulfate agar and Trypton Bilex-glucuronidase medium) were not different fromnTTC Tergitol 7 agar (TTC Tergitol 7 agar vs Chromocult Coliform agar, 294 samples, mean RD%n5.55; vs MLSA, 302 samples, mean RD% 1; vs TBX, 297 samples, mean RD% 22.78). The otherntwo alternative methods (Membrane Faecal coliform medium and Colilert 18/ Quantitray) gavensignificantly higher counts than TTC Tergitol 7 agar (TTC Tergitol 7 agar vs MFc, 303 samples,nmean RD% 8.81; vs Colilert-18/Quantitray, 76 samples, mean RD% 18.91). In other words,nthe alternative methods generated performance that was as reliable as, or even better than,nthe reference method. This study will help laboratories in Greece overcome culture and countingnproblems deriving from the EU reference method for E. coli counts in water samples.