Enumeration of Lactobacillus casei in the presence of L. acidophilus, bifidobacteria and lactic starter bacteria in fermented dairy products

Abstract

The aim of this work was to select a set of culture media to perform the enumeration of L. casei when it appears together with L. acidophilus, bifidobacteria and bacteria of lactic acid starters, in fermented dairy products. A number of L. acidophilus, Bifidobacterium and L. casei strains (8 of each) were tested for their ability to grow in two selective/differential media (LP-MRS agar and B-MRS agar). The enumeration of these bacteria using the media mentioned above was also carried out in fermented dairy products available on the market. B-MRS agar and LP-MRS agar were able to inhibit the lactic acid bacteria from the starters. B-MRS agar could be useful for the selective colony count of L. acidophilus or L. casei, or for a differential enumeration when these bacteria appear together in a fermented dairy product. In the case of bifidobacteria, a selective colony count could be performed on LP-MRS agar, even when it appears with L. casei, because a differential cell enumeration between both organisms was possible. The three probiotic bacteria could be simultaneously enumerated from dairy products that contain them along with starter bacteria using media developed in this work.