Standards Development

Scope

This document specifies requirements for the performance testing membrane filters intended for the
concentration and for direct enumeration afterwards of specific microorganisms and mixed populations
on solid media or on other solid devices containing media, for example absorbant pads.
It is not applicable for membrane filters used for concentration and elution or for qualitative methods.
These tests are applicable to all membrane filters intended for the microbiological analysis of different
kinds of water.
For example, these kinds of water include:
— drinking water, bottled water and other types of water with a low concentration of background
microorganisms;
— types of water with higher concentrations of background microorganisms, for example surface and
process water.
These tests are intended to demonstrate the suitability of the whole system - membrane filter together
with culture medium including the filtration step - required for the specific tests described in
International Standards. The membrane filters required for use are described in each specific standard.
This document applies to:
— manufacturers producing membrane filters;
— microbiological laboratories using membrane filters for their own testing or providing these to other
end users.

Purpose

The proposed document is based on the resolutions of the ISO/TC 147/SC 4 meeting on 2013-10-25 in Berlin where a NWI-Proposal on the revision of ISO 7704 was concluded.
The revision is intended to update and align some of the contents with ISO 8199:2018 and ISO 11133:
2014/Amd1:2018.
Membrane filters are used in all cultural techniques and also for many alternative techniques. In the
microbiology laboratory many tests and procedures depend upon membrane filter being consistent and providing reproducible results. Proficiency test schemes have indicated problems in the current use of combinations of membrane filters to be placed on media surface (e.g. PT scheme in Germany for routine application of ISO 11731 (Legionella in drinking water)). Membrane filters meeting established or minimal performance criteria are therefore a prerequisite for any reliable microbiological work. Sufficient testing should be carried out to demonstrate that a batch is ‘fit for purpose’ and that the filter can produce consistent results for the specific analysis used.

The revised standard will specify requirements for the performance testing membrane filters intended
for direct enumeration methods by microbiological culture methods.