MINERALS IN NUTRITION 39 



VII. IODINE AND BACTERIAL COUNTS IN MILK 



By James E. Fuller, Geo. S. Congdon, Myer Glickstein 



Departments of Bacteriology and of Dairy Industry 



The preceding section of this bulletin (Fuller and Esselen) enumerated 

 some of the experiments that have been made elsewhere as to methods of 

 increasing the iodine content of milk. Those experiments prompted the 

 study reported here concerning the effect of added iodine on the bacterial 

 content of milk. Two studies were made separately, that of Fuller and 

 Congdon in the Department of Bacteriology, and that of Glickstein in 

 the Dairy Department. The studies are briefly reviewed below. 



Fuller and Congdon. Three kinds of iodine were employed: tincture of 

 iodine and Lugol's solution, both made up according to the U. S. P. 

 standard; and a colloidal iodine preparation. Iodine Suspensoid, furnished 

 through the courtesy of Merck and Co., Inc., Rahway, N. J. The Suspen- 

 soid was the iodine preparation used by Devereux, referred to in reference 

 8 in the preceding section of this bulletin (Fuller and Esselen). 



The three kinds of iodine were added to samples of milk of graded 

 quality, and the milk was allowed to stand at room temperature. Samples 

 were plated, by the Standard Methods nf Milk Analysis teclinique, after 

 exposure periods of 30 minutes, 2^ hours, 4 liours, and 24 hours. 



It was found that the eflfectiveness of the iodine varied somewhat with 

 different samples of milk, even though their bacterial contents were similar. 

 This may have been caused by some of the iodine being absorbed by, or 

 combined with, protein and fat in the milk. It is obvious that milk samples 

 from different sources could have different fat and protein contents. In 

 general, it may be said that milk with low bacteria content required less 

 iodine than milk with high bacteria content to effectively control bacterial 

 growth. Milk samples with initial bacteria counts of 8,000 to 10,000 per 

 milliliter required from 280 to 300 parts per million of iodine, and milk 

 samples with counts around 50,000 bacteria per milliliter required over 

 500 parts per million of iodine to keep bacteria counts under control for 

 24 hours. 



Pure cultures of bacteria that may be encountered in milk were inoculated 

 into nutrient broth and into sterile milk. The bacterial species employed 

 were the colon bacillus and the typhoid bacillus, respectively representative 

 of normal and disease-producing intestinal bacteria; the aerogenes bacillus 

 and Bacillus subtilis, representative of air and dust-borne bacteria that are 

 harmless to health, but may spoil milk ; Staphylococcus aureus, a pus-form- 

 ing bacterium ; and Streptococcus lacfis. a normal milk-souring bacterium. 

 Less iodine was required to control bacteria in broth than in milk. Per- 

 haps this was because there is no protein or fat in the broth to inactivate 

 the iodine. Larger numbers of bacteria required larger quantities of 

 iodine for their control in either medium. 



The several bacterial species studied seemed to have about the same 

 degree of susceptibility to all three of the iodine preparations employed. 

 There was no particular choice among these iodine preparations, all being 

 about equally effective when results were determined on the basis of parts 

 per million of free iodine. The experiments indicated that the amount of 



