Staphylococcal Enterotoxin Detection in Cheese

A staphylococcal enterotoxins (SE) detection was performed in all cheese samples that presented Coagulase Positive Staphylococci levels ≥4.9 × 10⁴ cfu/g. For the detection of SE, ISO 19020:2017 [12 ] was followed. Briefly, 25 g of cheese (10% of the shell and 90% of the inner part) suspended in 40 mL of distilled water at 38 °C ± 2 °C were homogenized in a stomacher, for 1 min and then shaken in an VXR basic Vibrax orbital shaker (Ika^®, Staufen, Germany) at room temperature for 30 to 60 min to allow toxin diffusion. The pH of the slurry was adjusted between 3.5 and 4.0 with HCl and centrifuged at 3130× g for 15 min at 4 °C. The supernatant was collected and the pH adjusted to 7.5 ± 0.1 with NaOH and centrifuged again as described above. The supernatant was concentrated on a dialysis membrane with a molecular cut-off of 6000-8000 Da (Spectrum Laboratories, Rancho Dominguez, CA, USA) against 30% (w/v) of polyethylene glycol 20,000 (Merck, Darmstadt, Germany), overnight, at 4 °C. SE detection was performed using the alternative automated method VIDAS^® Staph enterotoxin II (SET 2) (bioMérieux).