20 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 



THE COLON TEST FOR EFFICIENCY OF PASTEURIZATION. 



In a study (6) of the ability of colon bacilli to survive pasteuriza- 

 tion it was found that certain strains could survive pasteurization at 

 145 F. for 30 minutes. On examining 174 cultures of colon bacilli it 

 was found that at 140 F., the lowest pasteurizing temperature, 95 

 cultures survived; at 145 F., the usual temperature for pasteuriza- 

 tion, 12 survived. In each case the heating period was 30 minutes. 

 Considerable variation was observed in the thermal death point of 

 the colon bacilli which survived at 145 F. When the cultures which 

 withstood the first heating were again heated it was found that many 

 did not survive, and in each subsequent heating different results 

 were obtained. Colon bacilli have a low majority thermal death 

 point but on account of the resistance of a few cells, they may survive 

 the pasteurizing process. 



The colon test as an index of the efficiency of the process of 

 pasteurization is complicated by the ability of certain strains to 

 survive a temperature of 145 F. for 30 minutes and to develop 

 rapidly when the pasteurized milk is held under certain tempera- 

 ture conditions met during storage and delivery. Consequently 

 the presence of a few colon bacilli in pasteurized milk under ordi- 

 nary market conditions does not necessarily indicate that the milk 

 was not properly heated. The presence of a large number of colon 

 bacilli immediately after the heating process indicates that the milk 

 has not been heated to 145 F. for 30 minutes and the test properly 

 applied should be valuable in control work. Fermentation tubes 

 can be used for making the test, but when gas formation is noted 

 the presence of colon bacilli should be demonstrated by further tests. 

 Often anaerobic spore formers are encountered which survive pas- 

 teurization and give the typical fermentation tube test. 



PAST AND PRESENT THEORIES OF PASTEURIZATION. 



pksteiiHzatlo^i at present^ looked upon with favor by medical 

 men, sanitarians, dairymen, and consumers, but the art has not been 

 developed without opposition, and its value is not universally ac- 

 cepted. Most of the objections to pasteurized milk have been based 

 on theory or on experiments in which the milk was pasteurized at 

 high temperatures. In view of our modern theories they are of no 

 great importance. 



One of the greatest objections to pasteurized milk has been that 

 the heating destroyed the lactic-acid bacteria and that putrefactive 

 organisms were left, which, when relieved from the restraining action 

 of the acid-forming bacteria, would develop, forming toxins and 

 putrefactive products. It was believed that the milk, because it 

 was not sour, would be consumed in that condition. This objection 



