Presentation at the 3 rd SAFOODNET seminar

Transcription

1 Sense and nonsense in standardisation Dr Rijkelt Beumer Laboratory of Food Microbiology Wageningen University (NL) Standardisation is a process in which on national, European or mondial level agreements are made between concerned parties about (technical) specifications of a product, a service, or an industrial process, with as most important goal: more efficiency and/or improvement of quality. 1 (18)

2 Methods can be a confusing and dangerous topic... there is a general law that governs methodology: Law of Confusion: M = N (18)

3 ... there is another general law that governs methodology: Microbiologists would rather use each other s toothbrushes than each other s methods Sense: Because we need standardised methods for research and trade 3 (18)

4 Nonsense: Because there are a lot of conflicting interests Criticisms * slowness in incorporation of new methods as standard reference methods * less harmonisation and dialogue between ISO and some other standards bodies such as AOAC * ISO methods never previously validated * national organisations push for methods to solve local problems * non vertical methods (i.e. horizontal) 4 (18)

5 Terminology terminology of culture media formulation of substances, in liquid, semi solid or in solid form, which contain natural and/or synthetic constituents intended to support the multiplication, (with or without inhibition of certain mo), identification or preservation of viability of microorganisms This presentations * who determines (standard) methods * who needs (standard) methods * what are standardised methods used for * horizontal versus vertical methods standardisation, impact and validation problems * which criticisms are valid 5 (18)

6 Who determines methods? * National bodies for standardisation (159 countries) o NEN o BIN o DIN o AFNOR o NMKL The Netherlands Belgium Germany France Scandinavian countries etcetera Who determines methods? * International Organization for Standardisation (ISO) * Technical committees for standardisation: ISO/TC 34 Agricultural food products * Subcommittee SC 9 Microbiology secretariat: France * Subcommittee SC 5 Milk and milk products * ISO/IDF/AOAC, tripartite agreement since 2004: ISO/IDF 6 (18)

7 Who determines methods? * Comité Européen de Normalisation (CEN) * Technical committee CEN/TC 275 Food analysis Horizontal methods * Study group (WG) 6 Microbial contamination * secretariat: France WTO Codex AOAC IDF industrial companies Microbiological methods: the stakeholders trade organisations national groups CEN EU ISO 7 (18)

8 Process to develop a new standard * New work item proposal (NWIP) * Working Document (WD) * Committee Draft (CD) * Draft International Standard (DIS) * Final Draft International Standard (FDIS) * International Standard * Revision New work item proposal (NWIP) voting within 3 months NWIP Microbiology of food and animal feeding stuffs Horizontal method for the enumeration of aerobic bacteria from surfaces using contact plates and swab methods 8 (18)

9 Working Document (WD) no voting period prepared by a project leader * detailed description of the method * apparatus necessary (rodac plate, swab, sponge, cloth, stomacher, pipettes, petri dishes, culture media, water bath, incubator etc. Committee Draft (CD) voting within 3 months * response of members (countries) * comments of members Project leader will adapt the CD and, thereafter, sent it to the secretariat: launch of Draft International Standard 9 (18)

10 Draft International Standard (DIS) voting within 5 months * member countries will give (detailed) comments * task of the project leader to approve or disagree * e.g include sponges * include hygiene scores * temperature of the water bath not correct (should be 45 47ºC and not 46 ±1ºC) Final Draft International Standard (FDIS) voting within 2 months * Only minor comments allowed, mainly on text * International Standard (will last for 5 years) * Revision after 5 years, sent as DIS 10 (18)

11 Example of a standard for Bacillus cereus * EN ISO 7932 General guidance for the enumeration of Bacillus cereus Colony count technique at 30 C * Usually ISO develops new standards and CEN will adapt these (to prevent separate standards) * Most European ISO members also CEN members Example of a standard: Bacillus cereus * EN ISO 7932 General guidance for the enumeration of Bacillus cereus Colony count technique at 30 C * Medium: Mannitol egg yolk polymyxine agar (MYP) * < tests for confirmation * Addition of precision data * ISO Horizontal method for the enumeration of low numbers of Bacillus cereus MPN technique 11 (18)

12 Example of a standard: Bacillus cereus Confirmation ISO 7932 (1993) * nitrate reduction * glucose fermentation * production of acetylmethylcarbinol (Voges Proskauer) Confirmation EN ISO 7932 Horizontal method for the enumeration of presumptive Bacillus cereus Colony count technique at 30 C * haemolysis on (sheep)blood agar plates What are standardised methods used for enforcement by official food controllers i.e. to answer the question is a certain (group of) m.o. present in this sample, or... is a certain (group of) m.o. present above a prescribed tolerated level for purposes of litigation/dispute are their salmonellae in halva? 12 (18)

13 What are standardised methods used for for comparing alternative methods in reality some (official) labs do not use the reference method (golden standard) on a daily basis * One of the major problems is that so called rapid methods should be validated against the golden standard. * However, the golden standard itself is a not validated method, usually accepted as the best method, but not proven. * Therefore, in all standard methods, precision data should be included 13 (18)

14 Example of a standard: Listeria monocytogenes * A nice example is the validation of PALCAM and Oxford, media used for the isolation and enumeration of Listeria monocytogenes * After performing a collaborative study (rather expensive), precision data were included in the standard * Values were quite low due to the disadvantage that these media have no elective feature to distinguish L. monocytogenes from non pathogenic listerias Example of a standard: Listeria monocytogenes In 1999 it was decided to start trials with chromogenic media and blood containing media for the detection and enumeration of L. monocytogenes enrichment (ALOA, Rapid L mono, BA... etc) enumeration (ALOA, Rapid L mono, BA... etc) ALOA performed best of all, some countries voted against: Sweden (own BA), Thailand etc (too expensive) (18)

15 Example of a standard: Listeria monocytogenes * To be part of an ISO standard, the composition of a medium should be known (no secret components), moreover (parts of) the medium should not be patented * Biolife, producer of ALOA, was willing to give its composition, and there was no patent * trials with home made ALOA Example of a standard: Listeria monocytogenes * three (3) years after the start of the first trials, it was decided to incorporate ALOA in the current standard, as medium of first choice. * manufacturers did complain: * there should be several formula of the medium * the medium was too difficult to prepare * there would be lack of phosphatidyl inositol (component for lecithinase C reaction) 15 (18)

16 Example of a standard: Listeria monocytogenes * in Bangkok (December 2002) participants agreed on resolution to incorporate ALOA in June 2004 oxoid biokar merck Example of a standard: Listeria monocytogenes Parma April 2003 * Several attempts made to change ALOA without former trials: replacement of phosphatidyl inositol by lecithin * trials with lecithin... if ok...incorporation at revision of the standard * a long winded process, and... new precision data are necessary!!! 16 (18)

17 Example of a standard: Listeria monocytogenes * replacement of phosphatidyl inositol by lecithin same results * a long winded process, and... new precision data are necessary!!! * Moreover: confirmation of characteristic colonies still necessary? No according to the manufacturers Yes according to ISO Example of a standard: Listeria monocytogenes Listeria catalase Gram stain (motility) Listeria monocytogenes haemolysis CAMP test acid from rhamnose and xylose 17 (18)

18 Example of a standard: Listeria monocytogenes presumptive L. monocytogenes Gram stain optional Haemolysis CAMP test if necessary Rhamnose Xylose other presumptive Listeria spp Gram stain Haemolysis CAMP test if necessary VP test further tests if specification needed Standardisation: horizontal or vertical * the perennial question why are we here? 18 (18)