Staphylococcal food poisoning (SFP) is a common food-borne illness most often associated with contamination during food handling. Approximately 20% of healthy people are persistent carriers of Staphylococcus aureus and about 80% of human nasal isolates of S. aureus harbor at least one gene for a Staphylococcal enterotoxin (SE) protein, with the genes for SEA for SEB detected most frequently. SEA and SEB are also most commonly associated with SFP. Additional risks for SFP are associated with certain types of foods; for example, mastitis in dairy cattle may lead to the contamination of raw milk by enterotoxin-producing S. aureus. Pasteurization conditions for raw milk have been established to minimize biological hazards while retaining nutritional quality. However, past studies have documented the resistance of Staphylococcal enterotoxin proteins to heat inactivation and the reactivation of their biological activities upon cooling. Differential scanning calorimetry (DSC) provides an important tool for the biophysical characterization of protein toxins. DSC was used to study the thermal stabilities of SEA and SEB and evaluate the reversibility of protein unfolding at pH 6.8 and 4.5, values selected to be consistent with whole milk and fermented dairy products, respectively. The thermal stability of SEA was greater at pH 6.8 than at pH 4.5 and there was no evidence for reversible protein refolding. In contrast, SEB exhibited enhanced thermal stability at pH 4.5 compared to pH 6.8 and reversible refolding was readily apparent at pH 4.5 but absent at pH 6.8. Maximal thermal stability and reversible refolding for SEB were observed at pH 3.5 – 4.0 in sodium acetate buffer. Phosphate impaired SEB refolding efficiency at pH 4.5 in sodium acetate buffer. Thus, the nature of a food matrix can affect the thermal stability of Staphylococcal enterotoxins and the efficacy of heat treatments designed to inactivate them.

Influence of pH on the thermal stability of Staphylococcal enterotoxins A and B and on the reversibility of protein refolding as measured by differential scanning calorimetry

256th National Meeting (2018)

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