TY - JOUR
T1 - Evaluation of the ISO 7932 standard for the enumeration of Bacillus cereus in foods
AU - Schulten, S. M.
AU - In't Veld, P. H.
AU - Nagelkerke, N. J.D.
AU - Scotter, S.
AU - De Buyser, M. L.
AU - Rollier, P.
AU - Lahellec, C.
N1 - Funding Information:
For acceptance of standards by the Comité Européen de Normalisation (CEN), methods need to be validated by means of a collaborative study. Until now this has not been done for any of the International Standards for detection or enumeration of micro-organisms in foods. Project no. SMT4-CT96-2098, financed by the European Commission (Standards, Measurements and Testing Program (SM&T)), was elaborated to determine the precision data of six ISO (International Organisation for Standardisation) methods with the highest priority for acceptance by CEN. These are Bacillus cereus (enumeration), Listeria monocytogenes (detection and enumeration), Staphylococcus aureus (enumeration), Clostridium perfringens (enumeration) and Salmonella (detection). Three contractors are involved in this project: Agence Française de Sécurité Sanitaire des Aliments, Département Hygiène, Qualité et Securité des Aliments (AFSSA – HQSA, Paris, France) also acting as co-ordinator of the project, Ministry of Agriculture, Fisheries and Food, Central Science Laboratory (MAFF-CSL, Norwich, UK) and the National Institute of Public Health and the Environment (RIVM, Bilthoven, The Netherlands). Each contractor is responsible as ‘trial leader’ for the validation of two of the ISO methods. Each method is validated by a collaborative trial according to a design which conforms to the rules of the International Harmonised Protocol for Collaborative Studies ( Anonymous, 1995 ). Data from the collaborative trials is used to calculate: (1) the precision of the quantitative methods in terms of repeatability (r) and reproducibility (R) in relation to food type and inoculum level; and (2) the performance characteristics relating to an ‘equivalent value’ of r and R appropriate to qualitative data using statistical models being developed as one of the objectives of this project. The results are intended for publication by CEN in the corresponding CEN methods and subsequently by ISO via the Vienna Agreement. The first method to be validated was the 1993 ISO 7932 standard for the enumeration of Bacillus cereus ( Anonymous, 1993 ), organised by the RIVM. The collaborative trial was carried out in October 1997.
PY - 2000/6/10
Y1 - 2000/6/10
N2 - Twenty, mostly European laboratories took part in a collaborative study to validate the general 1993 ISO 7932 standard for the enumeration of Bacillus cereus in foods (Anonymous, ISO 7932, Microbiology - General Guidance for the Enumeration of Bacillus cereus - Colony-count Technique at 30°C. International Organisation for Standardization, Geneva, Switzerland, 1993). The objective was to determine the precision data in terms of repeatability (r) and reproducibility (R) of the method using three different food types at various inoculum levels. The results are intended for publication in Comite Europeen de Normalisation (CEN) and ISO standards. The method was challenged with three types of food product: fresh cheese, minced beef and potato powder. Each participant received eight samples for each food type: blind duplicates at four inoculum levels (target values of B. cereus of 0, 103, 104 and 105-106 colony forming particles (cfp)/g). In addition, two reference materials (RMs, capsules containing milk powder, artificially contaminated with B. cereus) were included in the study. All test materials were tested extensively for homogeneity and stability prior to the collaborative trial. In addition to determining the precision parameters of the ISO method, polymyxin pyruvate egg yolk bromothymol blue agar (PEMBA, incubation at 37°C) was included in the study to evaluate possible differences in performance compared to mannitol egg yolk polymyxin agar (MEYP, incubation at 30°C) which is prescribed in the ISO standard. In this study no difference in performance between MEYP and PEMBA medium was observed. Results from the glucose fermentation confirmation test indicated that generally 48 h was needed to obtain a yellow colour throughout the whole test tube. A high number of false negative results with the Voges Proskauer (VP) reaction, even after 48 h of incubation of the tubes, was observed in some laboratories. Values for r and R were therefore calculated without VP test results. Further studies have been initiated by the ISO technical committee in order to improve the performance of the confirmation tests. The precision of the test method appeared to be unaffected by the type of food or the concentration of B. cereus present in the test sample. The overall repeatability value found for the food samples was 0.29log10 units and the overall reproducibility value was 0.42log10 units. For the reference material, the repeatability was 0.11log10 units and the reproducibility 0.22log10 units. It was recommended to CEN and ISO to include these values into the revised horizontal standard for the enumeration of Bacillus cereus. Copyright (C) 2000 Elsevier Science B.V.
AB - Twenty, mostly European laboratories took part in a collaborative study to validate the general 1993 ISO 7932 standard for the enumeration of Bacillus cereus in foods (Anonymous, ISO 7932, Microbiology - General Guidance for the Enumeration of Bacillus cereus - Colony-count Technique at 30°C. International Organisation for Standardization, Geneva, Switzerland, 1993). The objective was to determine the precision data in terms of repeatability (r) and reproducibility (R) of the method using three different food types at various inoculum levels. The results are intended for publication in Comite Europeen de Normalisation (CEN) and ISO standards. The method was challenged with three types of food product: fresh cheese, minced beef and potato powder. Each participant received eight samples for each food type: blind duplicates at four inoculum levels (target values of B. cereus of 0, 103, 104 and 105-106 colony forming particles (cfp)/g). In addition, two reference materials (RMs, capsules containing milk powder, artificially contaminated with B. cereus) were included in the study. All test materials were tested extensively for homogeneity and stability prior to the collaborative trial. In addition to determining the precision parameters of the ISO method, polymyxin pyruvate egg yolk bromothymol blue agar (PEMBA, incubation at 37°C) was included in the study to evaluate possible differences in performance compared to mannitol egg yolk polymyxin agar (MEYP, incubation at 30°C) which is prescribed in the ISO standard. In this study no difference in performance between MEYP and PEMBA medium was observed. Results from the glucose fermentation confirmation test indicated that generally 48 h was needed to obtain a yellow colour throughout the whole test tube. A high number of false negative results with the Voges Proskauer (VP) reaction, even after 48 h of incubation of the tubes, was observed in some laboratories. Values for r and R were therefore calculated without VP test results. Further studies have been initiated by the ISO technical committee in order to improve the performance of the confirmation tests. The precision of the test method appeared to be unaffected by the type of food or the concentration of B. cereus present in the test sample. The overall repeatability value found for the food samples was 0.29log10 units and the overall reproducibility value was 0.42log10 units. For the reference material, the repeatability was 0.11log10 units and the reproducibility 0.22log10 units. It was recommended to CEN and ISO to include these values into the revised horizontal standard for the enumeration of Bacillus cereus. Copyright (C) 2000 Elsevier Science B.V.
KW - Bacillus cereus
KW - ISO 7932
KW - Precision
KW - Repeatability
KW - Reproducibility
KW - Validation
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U2 - 10.1016/S0168-1605(00)00233-6
DO - 10.1016/S0168-1605(00)00233-6
M3 - Article
AN - SCOPUS:0034631362
SN - 0168-1605
VL - 57
SP - 53
EP - 61
JO - International Journal of Food Microbiology
JF - International Journal of Food Microbiology
IS - 1-2
ER -