Comparison of Enterolert?-E and ISO 7899-2 Membrane Filtration Method for theDetection of Enterococci in Water Samples

摘要

Enterococci spp. Is an indicator microorganism routinely tested in Europe for water quality. The current ISO method for the detection and enumeration of intestinalrnenterococci (method 7899-2) is a 48-hour membrane filtration method using Slanetz & Bartley medium followed by a two-hour confirmation procedure using bile-esculin-azide agar. Enterolert-E (IDEXX Laboratories, Inc. Westbrook, ME, USA) is based on IDEXX’s Define Substrate Technology for detecting Enterococci spp. In water samples. This medium when used with IDEXX’s Quanti-tray or Quanti-tray/2000 provides quantitative confirmatory results in 24 hours. Methods The Enterolert-E/Quanti-tray method was compared against the ISO 7899-2 method for quantitative detection of Enterococci spp. In drinking water samples in thernpresent study. Two hundred seventy-seven drinking water samples spiked with primaryrneffluents from different geographic locations in the United Kingdom were used to spikerndrinking water samples. The water samples were tested at IDEXX Laboratories, Inc.,rnWestbrook, ME, and at a laboratory in the United Kingdom. Duplicates of split samplesrnwere tested by both methods. For the ISO samples, 100 mL of spiked drinking waterrnwas filtered onto sterile 0.45 μm filters, and then placed on Slanetz & Bartely agar (S&B)rn(Oxoid LTD, Basingstoke, England). The agar plates were incubated at 36oC for 44rnhours +/- 4 hours followed by a transfer of the membranes onto bile esculin azide agarrn(BEAA) (Becton Dickson, Sparks, MD) at 44oC for 2 hours for confirmation (InternationalrnOrganization for Standardization, 2000). The Enterolert-E/Quanti-tray samples werernanalyzed by adding Enterolert-E to 100 mL of spiked drinking water, sealing thernsample/medium mixture in a Quanti-tray, and incubating the Quanti-trays at 41oC for 24rnhours. Fluorescent Quanti-tray wells were counted as positive for enterococci. ArnQuanti-tray MPN Conversion Table (IDEXX Laboratories, Inc.) was used to convert the number of positive Quanti-tray wells to MPN/100 mL. The ISO method 17994 was usedrnto compare the two methods (International Organization for Standardization, 2002).rnResultsrnThe upper and lower confidence intervals of the expanded uncertainty ofrnEnterolert-E results, when compared against the ISO 7899-2 method, were +18.5 andrn+2.0 respectively (Table 1). There is “no difference” between these two methods as setrnforth by the ISO method 17994.