Enumeration of Vjable Lactobacillus acidophilus Organisms in Dairy Products

Pasteurized low fat milk to which is added Lactobacillus acidophilus has now become a product of major volume on the U.S. market. The product contains millions of L. acidophilus per ml and is considered to be in the general category of cultured milk products for application of regulatory monitoring. There is a growing interest in developing standards for allowable minimum numbers of L. acidophilus in such products at point of sale. This can be accomplished best by use of a medium selective for lactobacilli such as Lactobacillus Selection Agar (LBS); non-selective media, such as APT agar, can also be used to enumerate L. acidophilus . The latter would provide less assurance that the counts were due to lactobacilli. The non-selectivity of APT, however, usually results in higher counts of L. acidophilus . There is need for application of accurate monitoring of such products to ensure the numbers as well as the identity of the culture used as the milk supplement.