ISO/CD 7899-3

Water quality — Enumeration of intestinal enterococci — Part 3: Most probable number method

Scope

This document specifies a method for the enumeration of intestinal enterococci in water. The method is based on the growth of target organisms in a liquid medium and calculation of the “Most Probable Number” (MPN) of microorganisms by reference to MPN tables or using informatic programs.

The test described in this document relies upon the detection of intestinal enterococci based upon expression of the enzyme ß-D-glucosidase. This method provides a confirmed result in 24 h with no requirement for confirmation of positive wells.

This method can be applied to a range of types of water (for example, drinking water, bathing water, groundwater, surface water and wastewater), including those containing an appreciable amount of suspended matter and high background counts of heterotrophic bacteria.

For marine waters, enterococci are best enumerated using diluted samples.