SURVIVAL OF TYPHOID BACILLI IN SOUR MILK

Abstract

C ERTAIN communities in our population make a practice of drinking milk permitted to undergo souring spontaneously. The question arose whether it is necessary to subject raw milk used for souring purposes to preliminary pasteurization in order to insure destruction of typhoid-paratyphoid group of bacilli, or whether any of those bacteria which might be-present would not be destroyed by acids developed in souring process. In order to answer this question a series of tests was arranged, results of which are given in tabulations of this paper. The subject of investigation is not wholly a new one, although practical point of departure of this study may be peculiar. A brief survey of earlier literature on subject includes following: Cautley (1) found that typhoid bacilli which had been added in large amount to milk could be demonstrated in living state for several days, and that viability of these organisms depended on number and character of contaminating bacteria. In sterilized milk typhoid bacilli were found to survive as long as four months, according to Bolley and Field (2). Fraenkel and Kister (3) added an enormous dose (2, and loops) to 10 cc. of buttermilk. At room temperature typhoid bacilli remained alive for three days, while at incubator temperature they died out after twentyfour hours. Bruck (4) endeavored to approximate natural conditions and recovered bacilli from sour cream for ten days after its separation from artificially infected milk. He also isolated them from buttermilk for same period of time and from butter, prepared from infected cream, for twentyseven days. Bassenge (5) states that typhoid bacilli are killed when acid production reaches 0.3 per cent to 0.4 per cent and is maintained there for twentyfour hours. This opinion is not shared, however, by many other workers. Krumwiede and Noble (6) say that the typhoid bacillus is gradually killed in sour cream by acids produced, rate of destruction being proportional to degree of acidity and number of typhoid, bacilli present. They find that typhoid bacilli are killed in about four days in a moderately contaminated cream, but that they will live longer if initial multiplication has occurred. Lactic acid in varying amounts was added to milk containing typhoid bacilli by Trillat and Fouassier (7), and its inhibitive effect demonstrated. They also made a comparative study of rate of multiplication of typhoid bacilli in broth and milk. In milk multiplication began at once, but in broth no development was noticed for twenty-four hours.