Longevity of Typhoid Bacilli in Cheddar Cheese

Abstract

An epidemic of 29 cases of typhoid fever was traced to cheddar cheese made from milk infected by a typhoid carrier. From the development of cases, the typhoid organism must have lived in the cheese for 63 days. Eighteen cheeses were made in the laboratory, infected artificially with B. typhosus, and tested daily by removing a core of cheese, plating on brom-cresol-purple lactose agar and recovering the organism in purity. The experimental data indicate that usually B. typhosus can not be recovered from cheddar cheese after the 8th day but at times it may live longer. Its survival is influenced by the bacterial flora of the milk. Apparently, degree of acidity and character of acid are important factors in destruction of B. typhosus in cheese. However, a specific acidity will not give uniform results, probably because different acids do not affect the organisms to the same degree and because the bacterial flora of the milk and the complex chemical constituents of cheese may counteract the effects of acidity differently in different lots of cheese.