Volume 96, Issue 5 p. 1090-1096

PCR-based detection of enterotoxigenic Staphylococcus aureus in the early stages of raw milk cheese making

D. Ercolini

D. Ercolini

Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare e Ambientale e di Igiene, Università degli Studi di Napoli ‘‘Federico II’’, Portici, Italy

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G. Blaiotta

G. Blaiotta

Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare e Ambientale e di Igiene, Università degli Studi di Napoli ‘‘Federico II’’, Portici, Italy

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V. Fusco

V. Fusco

Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare e Ambientale e di Igiene, Università degli Studi di Napoli ‘‘Federico II’’, Portici, Italy

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S. Coppola

S. Coppola

Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare e Ambientale e di Igiene, Università degli Studi di Napoli ‘‘Federico II’’, Portici, Italy

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First published: 01 March 2004
Citations: 31
Salvatore Coppola, Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare ed Ambientale e di Igiene, Via Università 100, I 80055 Portici, Italy (e-mail: [email protected]).

Abstract

Aims: To define PCR-based detectability of Staphylococcus aureus in raw milk and intermediate products of raw milk cheese making in the presence of a complex background microflora by targetting different specific genes harboured by a single strain.

Methods and Results: The strain Staph. aureus FRI 137 harbouring nuc, sec, seg, seh and sei genes was used in this study. Raw milk artificially contaminated by different concentrations of Staph. aureus FRI 137 was employed in dairy processing resembling traditional raw milk cheese making. Samples of milk and curds were PCR-analysed after DNA extraction by targetting all the above genes. The pathogen was detected when the initial contamination was 104 CFU ml−1 by amplification of nuc and seh genes. 105 and 107 CFU ml−1 were needed when seg or sei and sec genes were targetted, respectively. Enrichment cultures from raw milk and curd samples proved to increase the detection limit of 1 log on average.

Conclusions: The direct detection of the pathogen in the raw material and dairy intermediates of production can provide rapid results and highlight the presence of loads of Staph. aureus potentially representing the risk of intoxication. However, every target gene to be used in the analysis has to be studied in advance in a system similar to the real case in order to determine the level of contamination potentially predictable.

Significance and Impact of the Study: The detection in real dairy systems of significant loads of Staph. aureus by multiple targets PCR can be more accurate.