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Production of Staphylococcal Enterotoxin A in Cheddar and Colby Cheeses^1,2,3,

Department of Food Science and Industries, University of Minnesota St. Paul 55101
and Division of Microbiology, Bureau of Science, Food and Drug Administration,, Washington, D.C. 20204

ABSTRACT

Enterotoxin A production by Staphylococcus aureus in Cheddar and Colby cheeses was determined by inoculating milk with different initial S. aureus populations and making cheese using normal and inhibited starter cultures. Detectable amounts of enterotoxin A were observed more frequently in Colby than in Cheddar cheese, both made with normal starter. With initial S. aureus inocula of at least 35,000 to 250,000 per milliliter of milk, enterotoxin A was detected when at least 15 million S. aureus per gram in Colby and 28 million in Cheddar developed. Starter failure induced by lactic bacteriophage during the early stages of cheese-making (draining or prior), resulted in extensive growth of S. aureus and detectable enterotoxin A, even with initial S. aureus populations of 1 to 2 thousand per milliliter of milk. Under these conditions, minimal S. aureus populations associated with enterotoxin A were about 3 to 5 million pergram. Partial failure of mixed-type multiple-strain starter culture or late failure (beyond the milling in Cheddar cheese) of single strain starter culture also resulted in enterotoxin A without extensive growth of S. aureus, 3 to 11 million per gram. Enterotoxin A persisted for over 3 years in Cheddar cheese made with normal or inhibited starter.

¹ Paper 7508, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul.

² Taken from data submitted to the Graduate School faculty at the University of Minnesota by the senior author in partial fulfillment of the requirements for the Ph.D. degree.

³ This research project UI 00269 was supported in part by grants from the National Center for Urban and Industrial Health, USPHS and National Cheese Institute.

⁴ Present address: Department of Botany and Microbiology, Montana State University, Bozeman 59715.