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Applicability of Heat-Stable Deoxyribonuclease Assay for Assessment of Staphylococcal Growth and the Likely Presence of Enterotoxin in Cheese^1,2,

Department of Food Science and Nutrition, University of Minnesota, St. Paul 55101

ABSTRACT

The relationships between growth of Staphylococcus aureus and production of deoxyribonuclease and enterotoxin A in cheese were evaluated. Conditions of cheese manufacture, such as the nature of milk used (heated or raw), type of lactic starter, and degree of starter activity, influenced deoxyribonuclease production. There was a close correlation between the S. aureus population and deoxyribonuclease content (correlation .88 in Cheddar and Colby cheeses for normal or inhibited starter, and .85 in Brick cheese for normal starter). Conditions which affected deoxyribonuclease production also had a similar influence on production of enterotoxin A. Detection of the former is especially useful in cheeses which may have had a partial starter failure not detected by the usual criteria of starter activity such as the titratable acidity of whey or the final pH of cheese. While the viable S. aureus population declined during aging, both deoxyribonuclease and enterotoxin A persisted for an extended time (3 yr at 4.4 C) in cheese of normal or inhibited starter.

¹ Paper No. 8228 of the Scientific Journal Series, Minnesota Agricultural Experiment Station.

² This work was taken from a thesis submitted by B. R. Cords to the faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Master of Science.