Coliform Organisms in Certified Milk

While investigators agree that coliform organisms in milk are of little significance with respect to conditions of production, a number have suggested that colon counts on high quality milks may be of some value under certain conditions. Ayers and Clemmer (1918) and Sherman and Wing (1933) suggest that the presence of coliform organisms is significant only if the total bacterial count is less than 10,000, the milk is relatively fresh, and the holding temperature has been below 50'F. Certified milk is required to meet these conditions. The American Asso-ciation of Medical Milk Commissions has approved a standard of less than 10 coliform organisms per milliliter, and has recom-mended the use of desoxycholate agar mediums (Leifson, 1935) for plating. Two types of desoxycholate agar mediums are available commercially. These differ primarily in their con-centration of sodium desoxycholate. The higher concentration (0.1 per cent) is recommended for certified milk or when 1 ml. of whole milk is to be plated, while the medium with the lower concentration (0.05 per cent), so-called "desoxycholate-lactose agar " is to be used when diluted milk is plated. To obtain a comparison of the two desoxycholate mediums 80 samples of certified milk were plated in both. In addition 40 samples of producers ' raw, a relatively low quality milk, were carried through the same procedure. Sixty of the certified and all of the producers ' raw milks were also plated in eosin-meth-ylene blue agar. The results of the comparative tests are shown in table 1. For each kind of milk the average counts on desoxy-cholate agar were only about 62 per cent of those on desoxycho-late-lactose agar, even though the certified milks were plated