[Determination of staphylococcal enterotoxins A, B and C in foods using ELISA with labeled antigen]

The competitive ELISA (polystyrene balls) with labeled antigen according to Stiffler-Rosenberg and Fey (1978) was applied to the analysis of Staphylococcal enterotoxins (SE) A, B and C in food to see if the enterotoxin concentration corresponding to maximum limit for SEA and SEB (1 ng/g food and 10 ng/g food respectively) could be measured. The effect of various food ingredients on the quantitative determination of SE in single-step and two-step variants of competitive ELISA was investigated. Generally, the effect of food was the lowest in extracts of cheeses and the highest in extracts of meats and pasta products. All enterotoxins were equally affected. However, within the same type of food significant differences in binding of both labeled and unlabeled antigen were found. The effect of food components often depended on the assay variant; the extracts of cheese gave better results in the two-step and the extracts of pasta better results in the single-step ELISA. In some weak-positive extracts, false positive results could not be excluded. In the samples of cheese which were involved in food poisoning exclusively the enterotoxin type A was found (up to 30 ng/g). The recovery of added SE (1-10 ng/g food) ranged from 50-70% in cheese and was about 70% in pasta foods. The assay sensitivity in buffer ranged from 0.2 ng/ml for enterotoxins A and B and 0.3 ng/ml for enterotoxin C (20 ml sample) to 0.5 ng/ml for A and B and 0.6 ng/ml for C (5 ml sample) to 1 ng/ml for A and B and 2 ng/ml for C (1 ml sample). In food, especially in meat and pasta the detection limit was often higher. With some exceptions the required sensitivity for enterotoxin A (1 ng/g) could only be reached in cheese.