BS EN ISO 9308-1:2000 pdf – Water quality — Detection and enumeration of Escherichia coli and coliform bacteria — Part 1: Membrane filtration method.
This part of ISO 9308 describes a reference method (Standard Test) for the detection and enumeration of Escherichia coli and coliform bacteria in water for human consumption. The Standard Test has a low selectivity, allowing the detection of injured bacteria. Due to the low selectivity, background growth can interfere with the reliable enumeration of coliform bacteria and E. coli, for example in some drinking waters, like shallow well waters or surface waters. This method is not suitable for these types of water. The Standard Test is based on membrane filtration, subsequent culture on a differential agar medium and calculation of the number of target organisms in the sample. ˆ ‰ This part of ISO 9308 is especially suitable for waters with low bacterial numbers. In special cases in which information is needed quickly, it provides a rapid method (Rapid Test) for the detection of E. coli only within 24 h in water for human consumption. The Rapid Test is based on membrane filtration, subsequent culture under selective conditions and calculation of the number of E. coli in the sample. The Standard Test and the Rapid Test can be applied to other kinds of water provided that suspended matter or background flora does not interfere with filtration, culture and counting.
2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of ISO 9308. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO 9308 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO/IEC Guide 2, Standardization andrelatedactivities — Generalvocabulary. ISO 3696:1 987, Waterforanalyticallaboratoryuse — Specification andtestmethods. ISO 5667-1:1980, Waterquality— Sampling — Part1: Guidance on the design ofsampling programmes. ISO 5667-2:1991, Waterquality— Sampling — Part2: Guidance on sampling techniques. ISO 5667-3:1994, Waterquality— Sampling — Part3: Guidance on the preservation andhandling ofsamples.
3 Terms and definitions For the purposes of this part of ISO 9308, the terms and definitions given in ISO/IEC Guide 2 and the following apply. 3.2 coliform bacteria ?Standard Test? lactose-positive bacteria as defined in 3.1 which are oxidase-negative 3.3 Escherichia coli ?Standard Test? coliform bacteria as defined in 3.2 which also produce indole from tryptophan at (44,0 ? 0,5) °C within (21 ? 3) h 3.4 Escherichia coli ?Rapid Test? bile-resistant bacteria which also produce indole from tryptophan at (44,0 ? 0,5) °C within (21 ? 3) h 4 Principle 4.1 General description of the method The method is based on membrane filtration and consists of two parts, the reference Standard Test and the optional Rapid Test, which can be performed in parallel as described below. The Standard Test includes incubation of the membrane on a selective medium with subsequent further biochemical characterization of the typical lactose- positive colonies, leading to the detection and enumeration of coliform bacteria and E. coli within 2 d to 3 d. The Rapid Test consists of two incubation steps allowing the detection and enumeration of E. coli within (21 ? 3) h. If both tests, Standard Test and Rapid Test, are performed in parallel, the final result for E. coli shall be the higher of the two. 4.2 Filtration and incubation Test portions of the sample are filtered through membranes which retain the bacteria. One membrane (Standard Test) is placed on a selective lactose agar medium which is incubated at (36 ? 2) °C for (21 ? 3) h and one membrane (Rapid Test) on a casein (tryptic digest)-containing agar medium incubated at (36 ? 2) °C for 4 h to 5 h, followed by incubation at (44,0 ? 0,5) °C for 19 h to 20 h on an agar medium containing casein (tryptic digest) and bilesalts.