Feb. IS, X915 



Colon Bacilli and Pasteurization 



403 



B. coli coimmmis or communior type according to the studies of Rogers, 

 Clark, and Davis (7), also Rogers, Clark, and Evans (8). The three cultures 

 not typical were probably of the B. aerogcties type. The cultures were 

 heated in milk as previously described to temperatures ranging from 

 51.7° C. (125° F.) to 68.3° C. (155° F.). The results given in Table I 

 show the number and percentage of cultures which withstood the differ- 

 ent temperatures. 



Table I. — Effect of heat on colon bacilli — all cultures 



It is seen from the table that 95, or 54.59 per cent of all the cultures, 

 survived at 60° C. (140° F.). This is particularly interesting, since this 

 temperature is the lowest used in commercial pasteurization. When 

 heated to 62.8° C. (145° F.), 12, or 6.89 per cent, of the cultures survived. 

 This temperature of 62.8° C. (145° F.) maintained for 30 minutes is the 

 temperature generally used in the process of pasteurization. Only one 

 culture sur\'ived a temperature of 65.6° C. (150° F.), and this culture 

 when heated again failed to sun.'ive at this temperature. 



These results are shown more clearly in figure i, where they have been 

 plotted. One of the cultures was destroyed at a temperature as low as 

 54.5° C. (130° F.). It is interesting to note that at 60° C. (140° F.) 95 

 of the cultures survived, while at 62.8° C. (145° F.) a difference of only 

 2.8° C. or 5° F., only 12 sur\'ived. In other words, 87.3 per cent of the 

 cultures which survived at 60^ C. (140° F.) were destroyed at 62.8° C. 



(145° F-)- 



It is very evident from these results that colon bacilli may survive the 

 process of pasteurization when a temperature of 62.8° C. (145° F.) is used. 



VARIATION IN THE THERMAL DEATH POINT OF THE CULTURES 



In order to determine whether the colon bacilli which survive at 62.8° C. 

 (145° F.) would exhibit the same alnlity in repeated heatings, the same 

 cultures were reheated to that temperature six times, with the results 

 shown in Table II. 



