Examining Dairy Products for Members of the Escherichia-Aerobacter Group

Abstract

Although on theoretical grounds a plating method using a solid differential medium is preferable to a fermentation-tube method for detection of Escherichia-Aerobacter organisms in dairy products, E.M.B., Endo or bile-salt agars proved unsuitable, since only about 1/3 of the "typical" colonies could be confirmed. Results indicated that production of 10% or more gas in "brilliant green-bile 2% special" fermentation-tubes inoculated with 10-0.001 cc of milk and incubated 48 hrs. at 37[degree] C. is reasonable assurance of the presence of Escherichia-aerobacter organisms. Since the organisms in 10 cc of properly pasteurized milk rarely produce gas under these conditions, gas production usually indicates either improper pasteurization or re-contamination.