REQUIREMENTS FOR MEMBRANE FILTERS FOR MICROBIOLOGICAL CULTURE METHODS ACCORDING TO ISO 7704 XEBIOS DIAGNOSTICS GMBH

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1 REQUIREMENTS FOR MEMBRANE FILTERS FOR MICROBIOLOGICAL CULTURE METHODS ACCORDING TO ISO 7704 XEBIOS DIAGNOSTICS GMBH Xebios, Düsseldorf, 12th May, 2017 An-Institut der Bernd Lange Mitglied im DVGWInstitutsverbund

2 Influence of media/filter combinations Using the same method does not necessarily mean obtaining the same results Different media and membrane filter combinations may have a big influence on the results of a membrane filtration method Pictures: C. Schuster, FH Rhein-Main Comparison of diluted sewage plant outlet with different membrane / culture media combinations according to ISO

3 Different brands of cellulose nitrate filters on BCYE-agar 3

4 Different batches of the same cellulose nitrate filters 4

5 ISO ISO ( ) Microbiology of food, animal feed and water Preparation, production, storage and performance testing of culture media Chapter 7.3 Testing of culture media used for membrane filtration includes a reference to ISO 7704 Water quality; Evaluation of membrane filters used for microbiological analyses This standard is from March 1985! Especially accredited laboratories have to perform the performance testing of their culture media together with the membrane filters for all combinations and batches. The procedure described in ISO is not identical to the procedure in ISO 7704 Revision of ISO 7704 since

6 ISO 7704: Water quality Evaluation of membrane filters used for microbiological analyses ( ) Evaluation of the efficiency of membrane filters by Comparing the counts on spread or pour plates versus membrane filtration on the same non selective medium and/or Comparing the counts of specific microorganisms on spread or pour plates versus membrane filtration on the same selective medium and conditions, that are suitable for the test For each test 200 colonies on 5 replicates have to be counted. Membrane filters should have a recovery of 80 % compared to the counts on the spread or poor plates to be accepted. These specifications are not in accordance with ISO 11133! 6 6

7 ISO/WD 7704: Water quality Evaluation of membrane filters used for direct enumeration by microbiological methods Annex A: Evaluation has to be done for new types of membrane filters or change of the manufacturer or if verification has failed. 7

8 ISO/WD 7704: Water quality Evaluation of membrane filters used for direct enumeration by microbiological methods Annex A: Verification has to be done for every new batch of membrane filters. 8

9 ISO/WD 7704: Water quality Evaluation of membrane filters used for direct enumeration by microbiological methods The number of colonies that have to be used for inoculation of each module is given as a reference to ISO This means: A level of approximately 100 cfu is necessary to achieve sufficient precision. In many cases a practicable range of 80 cfu to 120 cfu per plate with a minimum of 50 cfu per plate should be used. It may be necessary to use more than one plate. In new specific standards (e.g. ISO or ISO ) the range of quantitative determination per plate or filter is given together with other performance data in an Annex of each standard. This may differ from the practicable range given in ISO The recovery range for acceptance is given in references to the specific standards or as a reference to Annex F of ISO (Legionella: 50 %, intestinal Enterococci: 50 %, C. perfringens: 50 %, E. coli & coliform bacteria: 70 %,...) 9

Membrane filter types in ISO 11731 In ISO 11731 two types of membrane filters are

Membrane filter for concentration and elution Polycarbonat or polyethersulfone

10 Membrane filter types in ISO In ISO two types of membrane filters are mentioned: 1. Membrane filter for concentration and elution Polycarbonat or polyethersulfone Diameter 47 mm to 142 mm Rated pore sizes of 0,2 µm As this type of filter is not intended for direct enumeration on a medium it is not covered by ISO 7704! 10

Membrane filter types in ISO 11731 In ISO 11731 two types of membrane filters are mentioned: 2.

11 Membrane filter types in ISO In ISO two types of membrane filters are mentioned: 2. Membrane filter for direct placing on culture media cellulose nitrate or mixed cellulose esters Diameter 47 mm to 50 mm Rated poor size of 0,2 µm to 0,47 µm This type is covered by ISO 7704! With friendly permission of Dr. Geronda Montalvo and Dr. Nandakishore Rajagopalan, Illinois Sustainable Technology Center, Illinois 11

12 Timeline for the revision of ISO 7704 Project started in 26th May, 2015 Convenor Barbara Gerten, co-convenor Simon in 't Veld Today we are in a preparatory stage and a working draft exists A committee draft (CD) shall be registered by 30th June, 2017 latest After a voting period of 3 month the CD will be published After 2 further voting periods for a draft international standard (DIS) and final draft international standard (FDIS) the standard will be published by 26th May,

Rheinisch-Westfälisches Institut für Wasser Beratungs- und Entwicklungsgesellschaft mbh Moritzstraße 26 45476

13 IWW Water Centre IWW Rheinisch-Westfälisches Institut für Wasserforschung gemeinnützige GmbH IWW Rheinisch-Westfälisches Institut für Wasser Beratungs- und Entwicklungsgesellschaft mbh Moritzstraße Mülheim an der Ruhr Telefon: +49 (0) Fax: +49 (0) Bernd Lange Dr. Peter Balsaa Telefon: +49 (0) Affiliated Institute of the Member of DVGW Alliance of Institutes

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Guideline Landscape. Quality Control Guideline Landscape Quality Control Environmental Water Testing Parma Biotec Watertesting according to current standards & regulations Membranefilteroverview for accredited laboratories ISO 7704:1985 QC