Abstract
Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus are involved in the manufacture of yogurt, and Bifidobacterium spp. can be supplemented if probiotic properties are expected. In such products, enumeration of each bacterial component is a hard task since they have similar nutritional requirements. For this reason, there is still no official and reliable methodology for this purpose. The objectives of the present study were to evaluate the most appropriate culture medium for the enumeration of four different Bifidobacterium species in the presence of S. thermophilus and L. delbrueckii subsp. bulgaricus isolated from commercial cultures and investigate the influence of different strains of S. thermophilus on the choice of medium. Among 11 isolates of S. thermophilus obtained from these cultures, and which were submitted to repetitive element sequence-based PCR (rep-PCR), nine were found to be distinct strains. For selective enumeration of the Bifidobacterium species, results were influenced by the S. thermophilus strain used, but De Man, Rogosa and Sharpe (MRS) agar containing bile salts showed the best results for all of the Bifidobacterium species. Key words: Bifidobacterium spp., Streptococcus thermophilus, culture media, selectivity.
Highlights
Evalua ation of o cultu ure me edia forr selec ctive en numerration of Bifiidobac cterium m spp. in com mbination witth diffe erent strains of Sttreptoc coccus s therm mophillus iso olated from com mmerc cial yog gurt sttarter c culture es
The choice of a selective medium for the enumeration of Bifidobacterium in the presence of a starter culture is dependent on the probiotic species present in the product
Commercial starter cultures may contain various S. thermophilus strains in their formulations, with different nutritional requirement and different sensitivity pattern to inhibitory compound, hindering the selection of the selective culture medium
Summary
Evalua ation of o cultu ure me edia forr selec ctive en numerration of Bifiidobac cterium m spp. in com mbination witth diffe erent strains of Sttreptoc coccus s therm mophillus iso olated from com mmerc cial yog gurt sttarter c culture es. Bulgaricus are involved in the Streptococc e suppleme manufacturre of yogurtt, and Bifido obacterium spp. can be ented if prob biotic prope erties are expected. In such prod ducts, enume eration of ea ach bacteria al componen nt is a hard ttask since they have similar nutrritional requirements. Bullgaricus iso olated from commercial cultures a and investiga ate the influ uence of different sttrains of S. thermophilus s on the choice of med dium. For se elective enumeration off the Bifidob bacterium species, results were influenced by y the S. therrmophilus sttrain used, b but De Man,, Rogosa and Sharpe (MRS) agar containing bile b salts sho owed the bes st results forr all of the Biifidobacteriu um species
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