ABSTRACT
Staphylococcal food poisoning outbreaks are a major cause of food-borne illness in the European Union and their notification has been mandatory since 2005. Criteria for the enumeration of coagulase-positive Staphylococci (CPS) and the detection of staphylococcal enterotoxins (SEs) in cheese have been set down in Commission Regulation EC 2073/2005. Currently, few information are available about the distribution of SEs in naturally contaminated cheeses, including raw-milk and artisanal dairy products. The aim of this study was therefore to investigate at both the CPS enumeration and the succession of the enterotoxigenic Staphylococcus aureus and produced enterotoxins levels on the rind and the core of a raw-milk semi-hard cheese, produced on farm. The study has been conducted in three steps: (I) seven wheels at different time of ripening where tested for the presence of SEs. (II) from each wheel, four portions were subsequently sampled from four different areas (peripheral rind, central rind, peripheral core and central core). (III) two cheese wheels, characterized by the highest and lowest CPS numbers and SEs quantification, based on the second step of the study, were further analyzed. A significant difference has been observed in the distribution of CPS and SEs in the four areas sampled, irrespectively of the batch and the time of ripening. The results of this study provided a set of previously unknown information on the influence of natural conditions on the distribution of CPS and SEs thereof in the cheese matrix, filling a gap in the understanding of SEs biosynthesis process.
ABSTRACT
An earlier intralaboratory validation study based on the EN ISO 16140 Standard conducted by the Community Reference Laboratory for coagulase-positive staphylococci including Staphylocococcus aureus showed that, after an extraction step using dialysis concentration, the Vidas SET2 detection kit could be used to screen staphylococcal enterotoxins in milk and milk products. In order to fully validate Vidas SET2, an interlaboratory study was organized. Six freeze-dried samples and 3 ready-to-use concentrated extracts were analyzed by 21 laboratories according to the method, including a detection with Vidas SET2. Results did not show false-positive or -negative results. Accordance and concordance parameters were equal to 100%, corresponding to a concordance odds ratio of 1. This interlaboratory study confirmed the satisfactory outcome of the preliminary tests and of the intralaboratory study performed previously. The Vidas SET2 detection kit can be used as a method for the detection of staphylococcal enterotoxins in milk and milk products as well as the Transia Plate SET detection kit in the European screening method for official control purposes, after an extraction step followed by dialysis concentration.
