4o6 microbiology of. milk and milk products 



Value of Bactesiological Milk Standards and Analyses 



Regarding the value of bacteriological standards for milk there is 

 still some difference of opinion among milk bacteriologists. The germ 

 content of any lot of milk is largely dependent upon three factors: the 

 number of organisms getting into the fresh milk; the temperature at 

 which it is kept; the age of the milk when analysis is made. 



The high bacterial count in any lot of milk may be the result of any 

 one of these conditions or a combination of them. A high count means 

 that there has been carelessness either' in the production, resulting in 

 high initial contamination, or in the subsequent handling permitting a 

 rapid multiplication of the organisms, or that the milk is old. 



On the other hand, milk with a low germ content can be obtained 

 only where the original contamination is small and the milk has been 

 held at low temperatures. A low count, therefore, means care both in 

 the production and later handUng of the milk. 



While the germ content may be regarded as a general index to the 

 care the milk has received, it may not at all indicate its wholesomeness. 

 A high count may be the result of the rapid growth of the lactic bacteria, 

 in which case the milk may be perfectly safe and wholesome. On the 

 other hand, the count maybe quite small but contain pathogenic species. 

 The bacteria count is valuable as showing the sanitary conditions of 

 production and handling, but much care should be used in the inter- 

 pretation of such results. In some ways a direct microscopic examina- 

 tion of the milk sediment is much more satisfactory. The skilled 

 analyst can recognize certain tj^es which may indicate the sanitary 

 quality of the milk. With suflScient experience one can recognize strep- 

 tococci, certain other groups and leucocytes. The presence and abun- 

 dance of one or more of these groups may indicate the nature of the 

 original contamination and the existence of diseases in the udders of 

 cows. If rightly interpreted the information thus obtained is of much 

 value. The weakness of this method lies in the fact that it is not always 

 possible to recognize the above types of organisms. In a smear prepa- 

 ration it is not possible to differentiate between pathogenic and non- 

 pathogenic streptococci or between B. coli and certain other types. 

 The presence of unusual numbers of streptococci and pus cells may 

 indicate the existence of disease in the cows and when this condition is 

 found in the milk it is often possible to trace it back to the farm and lo- 



