DIN EN ISO 14189:2016-11

Clostridium perfringens is widely recognized as a valuable indicator for faecal pollution. Within the intestinal tract of animals and man, these Gram-positive bacteria form spores which are resistant to heating compared with vegetative cells. C. perfringens in the intestine exists both as spores and vegetative cells, spores are also found in environmental samples. The spores of C. perfringens survive in water for months, much longer than vegetative faecal indicator bacteria and consequently their presence may indicate remote or intermittent faecal pollution. Monitoring of C. perfringens has proven useful for the assessment of the quality of water resources and to check the stages of water treatment to evaluate the treatment-works performance. The spores are not always inactivated by routine disinfection procedures (for example, chlorination). This International Standard specifies a method for the enumeration of vegetative cells and spores of Clostridium perfringens by the membrane filtration method in samples of water intended for human consumption. However, the method can be applied to all types of water samples provided they do not contain particulate or colloidal matter that interferes with filtration. A measured volume of the sample, or a dilution of it, is filtered through a membrane with a pore size of 0,45 μm sufficient to retain spores of clostridia. The membrane is incubated on a selective/differential agar (tryptose-sulfite-cycloserine agar) anaerobically at (44 ± 1) °C for (21 ± 3) h. C. perfringens usually produce black or grey to yellow brown colonies as a result of the reduction of sulfite to sulfide which reacts with a ferric salt in the medium. Characteristic colonies are counted and confirmatory tests are carried out. The result is calculated as the colony count per sample volume. If a count of spores alone is required the sample is first pre-treated at (60 ± 2) °C to inactivate vegetative bacteria. The text of ISO 14189:2013 has been prepared by Technical Committee ISO/TC 147 "Water quality" of the International Organization for Standardization (ISO) and taken over as EN ISO 14189:2016 by Technical Committee CEN/TC 230 "Water analysis", the secretariat of which is held by DIN (Germany). The responsible German committee is Subcommittee NA 119-01-03-03 UA "Mikrobiologie" ("Microbiology") of Working Committee NA 119-01-03 AA "Water examination" at DIN Standards Committee Water Practice (NAW).