The ISO 9308 standard, developed by the International Organization for Standardization (ISO), consists of the following sections under the main heading " Water quality - Counting of Escherichia coli and coliform bacteria":
The ISO 9308-1 standard describes a method for enumerating Escherichia coli (E. coli) and coliform bacteria. This method is based on membrane filtration, followed by culturing on chromogenic coliform agar medium and calculating the number of target organisms in the sample. Due to the low selectivity of differential agar medium, background growth prevents reliable enumeration of E. coli and coliform bacteria, for example, in surface waters or shallow well waters. This method is not considered suitable for such waters. The standard is particularly suitable for waters with low bacterial counts, resulting in fewer than 100 colonies on chromogenic coliform agar. These may include drinking water, disinfected pool water, or finished water from drinking water treatment plants. Some E. coli strains, such as Escherichia coli O157, which are beta-D-glucuronidase negative, are not detected as E. coli. Since they are beta-D-galactosidase positive, they appear as coliform bacteria on this chromogenic agar.
For the purposes of this standard,
The ISO 9308-2 standard describes a method for enumerating E. coli and coliform bacteria in water. This method relies on the growth of target organisms in a liquid medium and the calculation of the most likely number of organisms. This method is applicable to all types of water, including those containing significant amounts of suspended matter and heterotrophic bacteria with high background numbers. However, it should not be used for enumerating coliform bacteria in seawater. When used for enumerating E. coli in seawater, a 1/10 dilution in sterile water is generally required, although the method has been shown to work well with some seawaters that have lower than normal salt concentrations. In the absence of data to support the use of the method without dilution, a 1/10 dilution is used.
For the purposes of this standard,
The ISO 9308-3 standard describes a simplified method for the detection and enumeration of Escherichia coli in surface and wastewater by inoculation in a liquid medium. This method is applicable to all types of surface and wastewater, especially those rich in suspended matter. It is not suitable for drinking water or other water types where the guideline level is less than 15 per 100 ml. This method is also unsuitable for the enumeration and detection of coliform bacteria other than E. coli.
For the purposes of this standard, escherichia coli refers to beta-D-glucuronidase-positive microorganisms growing at an incubation temperature of 4 degrees in specified liquid medium containing 44-methylumbelliferyl-beta-D-glucuronide.
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