Probiotic characterization of Bifidobacterium spp. isolated from commercial fermented milk in the UK
The aim of this research was to study the identity and survival of probiotic bifidobacteria in fermented dairy products from the UK market throughout their shelf- life and carry out in vitro studies on some of the probiotic criteria and potential functional properties of the isolates including resistance to stomach-intestine conditions, antimicrobial activities, antibiotic resistance/susceptibility, antibiotic resistance genes and their transferability, biofilm formation and production of health- promoting secondary metabolites, such as conjugated linoleic acid (CLA). The initial study for choosing the right selective medium for isolation and enumeration of bifidobacteria included a comparative study on selectivity of well known media transgalactosylated oligosaccharides-mupirocin lithium salt (TOS- MUP) and Bifidobacterium iodoacetate medium 25 (BIM-25). Considering selectivity of the medium, recovery of the bifidobacteria and ease of preparation, it was concluded that TOS-MUP is the medium of choice for determination of total viable counts of bifidobacteria in fermented milks. The result of enumeration study indicated that most of the tested products (22 out of total 24) on TOS-MUP comply with the recommended minimum therapeutic level for probiotics (106 CFU/g) at the time of purchase and at the end of their shelf-life. All presumptive Bifidobacterium isolates were identified as Bifidobacterium animalis subsp. lactis by analysis of partial sequences of the 16S ribisomal RNA gene. Further use of rep-PCR for differentiation of all isolates using two different primers (GTG-5 and BOXA 1 R) did not show any difference among tested isolates as all isolates presented the same band profile. As far as the claims on the label are concerned, most of the products (19 out of 24) failed to name the Bifidobacterium species at all or correctly.
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