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

Abstract

Milk produced by cows infected with brucellosis was inoculated with a freshly isolated culture pf B. abortus to give about 1000 organisms per ml. The milk was made into cheddar cheese and the organisms survived in the cheese for 6 months at 4.4[degree] C, but all cheeses were negative in 1 yr. as detd. by guinea pig inoculation. When milk produced by reacting cows, selected to give high natural infections of 700-800 B. abortus organisms per ml., was made into cheese, this pathogen survived for 3 months in the cheese but not for 6 months. Commercial cheese milk selected at random and also from areas in which the cattle were known to have brucellosis was used for survey expts. 59 vats of commercial cheese milk gave 11 milks positive for B. abortus. There were 3 vats of positive milk that gave negative fresh cheese curds and this included 2 limburger cheeses. The cheddar cheeses from the 9 positive milks were all negative on first examination after storage at 1.1[degree] to 2.7[degree] C for periods of 41-84 days. No B. abortus organisms were recovered from any sample of cheese. The data show that an aging period of 60 days is reasonable assurance against the presence of viable B. abortus in cheddar cheese.