The Occurrence and Survival of Brucella Abortus in Cheddar and Limburger Cheese

Abstract

Most dairy products reach consumers after being subjected to a heat treatment sufficient to destroy any pathogenic bacteria that might be present, but there is still much unpasteurized Cheddar cheese made from raw milk. Since such cheese has not been found to cause undulant fever in man, one might reasonably expect that Brucella abortus dies or becomes non-infectious during normal cheese curing. I t is known that the dairy cows of the United States are often infected and that infected cows often give milk containing these bacteria. Conditions in the early stages of the manufacture of Cheddar cheese favor bacterial development and the bacteria are concentrated in the fresh curd. Some of the cheese might be infected so the question of the survival of Brucella abortus in Cheddar cheese has public health significance. This study was undertaken to show the lengt]~ of time that Brucella abortus survives in Cheddar cheese. First a preliminary survey was made on cheese milk in New York State. Then a study was conducted on cheese made from milk inoculated with cultures of the organism recently isolated from naturally infected milk. Tests were made on cheese manufactured from milk from selected reacting cows that were found by test to be producing milk heavily infected with Brucella abortus. Finally, a survey was conducted showing the contamination naturally occurring in milk of cheeseproducing areas in New York and Wisconsin, where brucellosis had not been eradicated from the dairy herds and the survival of Brucella abortus in naturally infected commercial Cheddar cheese was determined.