Statistical approach to validate the reduction in Venus gallina sample size for enumeration of E. coli according to ISO/TS 16649-3.

Autor: Ottaviani, Donatella, Parmegiani, Sonia, Chierichetti, Serena, Rocchegiani, Elena, Leoni, Francesca, Naceur Haouet, M., Latini, Mario
Zdroj: Accreditation & Quality Assurance; Dec2015, Vol. 20 Issue 6, p505-509, 5p
Abstrakt: Venus gallina is a small species of clam which is widespread in the Adriatic Sea. Because of the size of this shellfish, the preparation of samples in accordance with the mandatory standard method (ISO 6887-3) for the enumeration of Escherichia coli by the five-tube, three-dilution most probable number ( MPN) method (ISO TS 16649-3) is very time-consuming and labor-intensive. This paper describes the statistical approach adopted by the Italian Reference Laboratory for Bacteriological Contamination of Bivalves (NRL) to evaluate whether the use of a smaller sample size (25 g) of V. gallina for the enumeration of E. coli has an impact on the final results in comparison with sample size of 100 g as recommended in ISO 6887-3. The experimental design provided for the enumeration of E. coli on spiked and naturally contaminated samples was equally applied for samples of 25 and 100 g of flesh and liquor, respectively. The reproducibility limit and expanded uncertainty of spiked samples were both lower than those defined by the NRL in the phase of primary validation of method. For each level of experimental contamination, difference of the logarithms of arithmetic averages of the MPN of E. coli per 100 g obtained from 100-g and 25-g samples was lower than the reproducibility limit obtained in the primary validation. Moreover, the arithmetic averages of the MPN of E. coli per 100 g obtained from 100-g and 25-g samples for each level of experimental contamination were not significantly different ( P > 0.05). For naturally contaminated samples, each difference of logarithmically transformed values of MPN of E. coli per 100 g obtained from 100-g and 25-g samples was lower than the reproducibility limit of the primary validation. These results indicate equivalence between the MPN of E. coli per 100 g obtained processing 100 g and 25 g of V. gallina. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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