ABILITY OF COLON BACILLI TO SURVIVE 

 PASTEURIZATION 



By S. Henry Ayers, Bacteriologist, and W. T. Johnson, Jr., Scientific Assistant, 

 Dairy Division, Bureau of Animal Industry 



INTRODUCTION 



The presence of colon bacilli in pasteurized milk is generally inter- 

 preted as meaning either that the milk was not properly heated or that 

 it was reinfected after pasteurization by careless handling. This inter- 

 pretation is based on the low thermal death point of cultures of Bacillus 

 coli. 



Van Geuns (4)' in 1899 found that the Bacillus neapolitanus of Emme- 

 rich, the same organism as the B. coli communis of Escherich, was de- 

 stroyed by heating for five minutes at 59° C. (138.2° F.) and one minute 

 at 62.5° C. (144.5° F.). Based on the work of Van Geuns, Ringeling (6) 

 examined 75 samples of pasteurized milk from 24 dairies in Amsterdam 

 for the presence of colon bacilli. In 16 per cent of the samples exam- 

 ined he found B. coli present. Since colon bacilli were found in pas- 

 teurized milk from 10 of the 24 dairies, Ringeling concluded that this 

 proportion (41 per cent) of the dairies in Amsterdam did not pasteurize 

 or handle the milk properly. 



During recent years numerous investigators have studied cultures of 

 B. coli and found that the organisms were easily destroyed at tempera- 

 tures below 60° C. (140° F.), which is the lowest pasteurizing tempera- 

 ture. 



In a previous study by the writers (i ) of the bacteria which survive pas- 

 teurization 1 9 samples of raw milk in sterile flasks were heated for 30 

 minutes at 62.8° C. (145° F.). Each sample after pasteurization was 

 examined carefully for the presence of colon bacilli, but none were found. 



All these results naturally strengthened the opinion that the presence 

 of B. coli in pasteurized milk might be a valuable index as to the efficiency 

 of the process and the care observed in handling the milk after the heat- 

 ing process. 



At times, however, it has been found that high temperatures were re- 

 quired to destroy cultures of B. coli. Gage and Stoughton (3) in a study 

 of the resistance of B. coli to heat found that sometimes cultures were 

 destroyed only by heating to temperatures much higher than the usual 

 thermal death point. Heat-resistant strains have been also found by 

 De Jong and De Graaff (5). Certain strains with which they worked re- 



' Reference to "Literature cited" is made by number, p. 409. 



Journal of Agricultural Research, Vol. Ill, No. 5 



Dcpt. of Agriculture. Wnshjngton. D. C. Feb. is. 1915 



(401) 



A-13 



