Multilocus restriction typing: A tool for studying molecular diversity within Lactobacillus helveticus of dairy origin

Forty-two Lactobacillus helveticus strains isolated from two whey starter cultures and three cheeses were typed by multilocus restriction typing (MLRT), analyzing the restriction fragment-length polymorphism of PCR products generated from eight loci of housekeeping genes: β-galactosidase, lactose permease, UDP-galactose-4 epimerase, β-galactosidase transcriptional regulator, D-lactate dehydrogenase, peptidase N, stress-inducible protein and S-layer protein. MLRT analysis indicated wide strain heterogeneity. Strains were grouped according to their source of isolation. The low intra-species polymorphism detected in the 16S rRNA gene did not allow grouping of the strains with the same sensitivity reached by MLRT of protein-coding genes. This is the first demonstration of MLRT as a technique for the discrimination of Lb. helveticus strains; this technique is a promising tool to evaluate genetic diversity of related strains from different ecological niches.