12 



BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 



HOW MANY ORGANISMS OF THE COLON-AEROGENES GROUP CAN BE 

 INTRODUCED INTO MILK DURING MILKING? 



In order to interpret the significance of the colon count it is neces- 

 sary to know not only that organisms of the colon-aerogenes group 

 are always introduced into milk, but also in what numbers under 

 both normal and abnormal conditions. In determining the numbers, 

 the colon count has been made on a great many samples produced 

 under different conditions. The results of these examinations have 

 been summarized and are presented in Table 7. They are discussed 

 briefly at this point in order to emphasize the fact that under normal 

 conditions small numbers of organisms of the colon-aerogenes group 

 are found in fresh milk. The averages given for the colon-aerogenes 

 group are based on those samples showing the presence of colon 

 bacilli in 1/100 of a cubic centimeter. Included in the table are the 

 results of the examination of 1 4 samples of certified milk, which were 

 examined at the time of delivery to the consumer. Except for the 

 certified milk all the data presented in the table are based on the 

 examination of milk produced under controlled conditions from 4 

 cows kept in a small experimental barn. The condition of the barn 

 and the cows was changed at times from clean to extremely dirty 

 in order to suit the purpose of the experiments. The handling of 

 the utensils was also varied for similar reasons. 



Table 7. — Summary of colon-aerogenes contamination under different conditions of 



milk production. 



Conditions of milk production. 



Samples 

 exam- 

 ined. 



Colon-aerogenes 



organisms in 



1/100 c. c. 



Range of 



colon 



counts. 



Average 

 colon 

 count. 



Number. 

 14 



Number. 

 i 



Per cent. 

 



Per c. c. 

 1-20 



Per c. c. 

 



86 



6 



6.9 



100-200 



116 



56 



6 



10.7 



100-400 



183 



84 



24 



28.6 



( 2 ) 



( 3 ) 



28 



20 



71.4 



100-1,800 



750 



Average 



total 

 bacteria. 



Certified milk as delivered 



Clean barn, clean cows, sterilized uten- 

 sils (A) 



Dirty barn, dirty cows, utensils ster- 

 ilized (B) 



Dirty barn, dirty cows, utensils washed 

 at once after milking, but not sterilized 

 (C) 



Dirty barn, dirty cows, utensils held 

 for 8 hours before washing, and not 

 sterilised (D ) 



Per c. c. 

 10, 471 



6,091 



36,541 



465,086 



1,299,000 



1 7+ in 1 cubic centimeter. 



2 23 samples, 100-2,000. 1 sample, 28,400. 



8 Average of 23 samples, 557. Average of 24 samples, 1,717. 



The examination of 86 samples of milk produced in a clean barn, 

 from clean cows, and with sterilized utensils, is shown in Table 7. 

 The term "sterilized" signifies steamed for 20 to 30 minutes. That 

 the milk produced under these conditions was of high quality from a 

 bacterial standpoint is shown by the average total count of 6,091 per 

 cubic centimeter. Only 6 samples of the 86, or 6.9 per cent, con- 

 tained organisms of the colon-aerogenes group in 1/100 of a cubic cen- 

 timeter. The number of these organisms in the 6 samples ranged 

 from 100 to 200 and averaged 116 per cubic centimeter. 



