The use of mupirocin for selective enumeration of bifidobacteria in fermented milk products

The susceptibility to mupirocin in 15 bifidobacteria strains and 14 lactic acid bacteria strains were tested. In the Wilkins-Chalgren broth the growth of lactobacilli, lactococci, leuconostocs, and streptococci was inhibited at mupirocin concentration as low as 0.625-40 mg/l. On the other hand, the growth of bifidobacteria in the same medium was not influenced by mupirocin at a concentration of 300 mg/l. Subsequently, a selective medium, Wilkins-Chalgren agar containing mupirocin (100 mg/l), was developed for the isolation and enumeration of bifidobacteria in fermented dairy products. Strains of lactobacilli, lactococci, leuconostocs, and streptococci were completely inhibited on this selective medium. On the contrary, recovery rates of bifidobacteria on this medium were around 100%. It could be concluded that the new medium is highly selective and permits the growth of all common strains of bifidobacteria. The new medium can also be applied as a selective medium for bifidobacteria in probiotics that contain mixed population of lactic acid bacteria and bifidobacteria. A further advantage of this medium is its ease of preparation.