title: Comparison of Colilert-18 with miniaturised most probable number method for monitoring of Escherichia coli in bathing water.
abstract: The purpose of this equivalence study was to compare an alternative method, Colilert-18 Quanti-Tray (ISO 9308-2) with the European bathing water directive (2006/7/EC) reference method, the miniaturised most probable number (MMPN) method (ISO 9308-3), for the analysis of Escherichia coli. Six laboratories analysed a total of 263 bathing water samples in Finland. The comparison was carried out according to ISO 17994:2004. The recovery of E. coli using the Colilert-18 method was 7.0% and 8.6% lower than that of the MMPN method after 48 hours and 72 hours of incubation, respectively. The confirmation rate of presumptive E. coli-positive wells in the Colilert-18 and MMPN methods was high (97.8% and 98.0%, respectively). However, the testing of presumptive E. coli-negative but coliform bacteria-positive (yellow but not fluorescent) Colilert-18 wells revealed 7.3% false negative results. There were more false negatives in the naturally contaminated waters than in the samples spiked with waste water. The difference between the recovery of Colilert-18 and the MMPN method was considered not significant, and subsequently the methods are considered as equivalent for bathing water quality monitoring in Finland. Future bathing water method equivalence verification studies may use the data reported herein. The laboratories should make sure that any wells showing even minor fluorescence will be determined as positive for E. coli.
authors.affiliation: Water and Health Unit, The National Institute for Health and Welfare, PO Box 95, 70701 Kuopio, Finland E-mail: tarja.pitkanen@thl.fi; Department of Environmental Science, University of Eastern Finland, Kuopio Campus, PO Box 1627, 70211 Kuopio, Finland.
authors.forename: Ananda
authors.initials: A
authors.lastname: Tiwari
authors.affiliation: Pikkukoskentie 3, 00650 Helsinki, Finland.
authors.forename: Seppo I
authors.initials: SI
authors.lastname: Niemelä
authors.affiliation: Water and Health Unit, The National Institute for Health and Welfare, PO Box 95, 70701 Kuopio, Finland E-mail: tarja.pitkanen@thl.fi.
authors.forename: Asko
authors.initials: A
authors.lastname: Vepsäläinen
authors.affiliation: Ministry of Social Affairs and Health, Meritullinkatu 8, 00170 Helsinki, Finland.
authors.forename: Jarkko
authors.initials: J
authors.lastname: Rapala
authors.affiliation: Metropolilab, Viikinkaari 4, 00790 Helsinki, Finland.
authors.forename: Seija
authors.initials: S
authors.lastname: Kalso
authors.affiliation: Water and Health Unit, The National Institute for Health and Welfare, PO Box 95, 70701 Kuopio, Finland E-mail: tarja.pitkanen@thl.fi.
authors.forename: Tarja
authors.initials: T
authors.lastname: Pitkänen
mesh_terms: D001494:Baths; D015169:Colony Count, Microbial; D004784:Environmental Monitoring / Q000379:methods*; D004926:Escherichia coli / Q000302:isolation & purification*; D014871:Water Microbiology; D060753:Water Quality