Thermoduric Bacteria in Pasteurized Milk. II. Studies on the Bacteria Surviving Pasteurization, with Special Reference to High-Temperature, Short-Time Pasteurization

Abstract

The recent interest in thermoduric bacteria in milk has been stimulated especially by the development of modern methods for high-temperature short-time pasteurization; the adoption of tryptone glucose extract milk agar as the standard medium for plate counts ; agitation for the substitution of 32 C. (89.6 F.) instead of 37 C. (98.6 F.) for incubation of plate counts; and more stringent bacterial standards by certain Departments of Health. The first three tend to give higher counts with many milk supplies, which makes it difficult for the industry to meet the desires of the Health Departments for lower counts. Breed (1) has pointed out the desirability of concentrating efforts "on the extension of pasteurization as a blanket means of protection against milk-borne diseases and upon the eradication of diseases that may be transmitted to human beings from our milk-producing herds" before spending "an undue amount of energy and valuable time in getting some harmless types of bacteria out of our milk supplies. These bacteria are usually detected only because of the fact that they are difficult to kill during the pasteurization process." However, so long as pressure for very low bacteria counts is put on the industry by Health Departments, thermoduric bacteria present a serious problem, and their elimination from the milk supply must be undertaken.