Enumeration, isolation, and identification of bifidobacteria from dairy products

Abstract

Six dairy products were tested. Bifidobacteria were enumerated and isolated using TPY agar modified by the addition of mupirocin (100 mg l–1). Isolates were identified to the genus level by the detection of fructose-6-phosphate phosphoketolase (F6PPK) and by the FISH method. Bifidobacteria were characterised using API 50 CHL and API ID 32 A Rapid tests. In addition, grow at 46 °C was tested. Subsequently, all strains were identified to the species level using computer program Bacter. The identification was also carried out by PCR method using genus- and species-specific primers. The bifidobacterial counts in products tested varied from 2.37 to 7.17 log CFU/ml. High selectivity was seen for modified TPY agar from which all isolates were identified as bifidobacteria. While most strains were identified as B. animalis using Bacter program, the same isolates had positive reaction with B. lactis-specific primers. Strain isolated from Rajo yogurt was identified as B. longum by Bacter as well as using PCR, but its bacterial counts were too low. Our results showed, that most of the bifidobacterial strains currently used in food products could be of animal origin.

Keywords

• milk products
• dairy products
• microbiology
• bifidobacteria
• enumeration
• identification