Psychrophiles in Milk Held Two Days in Farm Bulk Cooling Tanks

Predominant psychrophilic bacteria were isolated from 174 samples of every-other-day milk from bulk milk cooling tanks from 12 farms producing Grade A milk. The 220 isolates so obtained were identified as to genus and species as far as possible. For the most part they fell into the genera Aerobacter, Alcaligenes~ Arthrobacter~ Flavobacterium~ Microeoccus, and Pseudomonas. Species o these genera are listed. Not all of the species could grow in pasteurized milk within three days at the cooling tank temperature of 38 F. (3.3 C.), although they formed colonies in seven days at 5 C. on plate count agar, and most of them could grow in pasteurized milk at 45 F. (7.2 C.) All of the species grew little, if any, in raw milk in the cooling tanks at 38 F.