Studies on Psychrophilic Bacteria. I. Distribution in Stored Commercial Dairy Products

Psychrophilie microorganisms capable of dominating the population in commercially pasteurized samples of milk, cream, chocolate drink, and cottage cheese after storage at 4 C. were isolated and characterized. Of 586 cultures, 70.6% were species of the genera Pseudomonas, 7.9% Alcaligenes, 9.2% Achromobacter, and 0.7% Flavobacterium; 10.8% were coliform bacteria and 0.8% yeasts. Distribution among the products, and between summer and winter samplings, was substantially uniform. Some factors underlying the discrepancies evident in the literature on the nature and distribution of the psychrophilic nficroflora of dairy products are discussed.