Quantitative analysis and molecular typing with pulsed-field gel electro-phoresis of two probiotic Lactobacillus strains from sour milk products available on the Swiss food market

摘要

From 13 sour milks of two producers supplemented with either Lactobacllus johnsonii (LC1) or Lactobadllus rhamnosus (LGG), counts of active microorganisms were measured on MRS agar. In each case, the legal minimal requirement of 10~6 living cells of the probiotic microorganism per gram of product at the end of the expiry date was met. From all the analyzed samples, the probiotic strains were isolated for subsequent typing. As typing method, pulsed-field gel electrophoresis (PFGE) was evaluated with 53 epidemiologically non-related strains of L. rhamnosus and found to be highly discriminating and reproducible. All LC1 or LGG strains isolated from products could be shown to have the same PFGE-profile as the corresponding reference strains. These results identified PFGE as a suitable tool to identify probiotic lactobacilli in the context of official food control and for epidemiological trace back. Finally, considerations with regard to the legal regulation of probiotic products, including analytical procedures for strain identification, were made.