Spontaneous Lactobacillus delbrueckii phage-resistant mutants with acquired bile tolerance

GUGLIELMOTTI, D.; BRIGGILER MARCÓ, M.; VINDEROLA, C.; DE LOS REYES GAVILÁN, C.; REINHEIMER, J.; QUIBERONI, A.

INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY

Elsevier

Año: 2007 p. 236 - 242

0168-1605

Three commercial phage sensitive strains of Lactobacillus delbrueckii (strains Ab1, YSD V and Ib3) and four spontaneous phage resistant mutants (strains A7, A17, V2 and I39) isolated from them, with a probiotic potential previously demonstrated, were studied by focusing on their tolerance against bile salts (ox gall). MICs (Minimal Inhibitory Concentrations) ranged from 0.30% to 0.35% (w/v) of ox gall. These strains were exposed to gradually increasing concentrations of ox gall with the aim of isolate bile resistant derivatives. Stable derivatives able to tolerate up to 0.9% of ox gall were obtained from L. delbrueckii Ab1, as well as from its spontaneous phage resistant mutants A7 and A17. Random Amplified Polymorphic DNA (RAPD-PCR) analysis revealed a strong genetic homology between the ox gall-tolerant derivatives and their respective non-adapted original strains. These derivatives maintained, in general, the phage resistance phenotype of the non-adapted strains, with only one exception (phage resistant mutant A7). After progressive ox gall adaptation, the phage resistant mutant A7 exhibited also a progressive reversion of the phage resistance phenotype. The derivative with the higher ox gall-acquired tolerance (A70.9) became sensitive to the phage, but derivatives with low (A70.3) and intermediate (A70.6) ox gall-acquired tolerance retained phage resistance. Technological properties of ox gall derivatives were comparable to those of their respective parent strains. However, the cells of the former were smaller than those of the original strains. Finally, the tolerant derivatives were faster to growth in the presence of ox gall than parent strains. Our results demonstrated that it was possible to obtain, by natural selection strategies, probiotic strains with an improved phage resistance, adequate technological properties and ox gall-tolerance acquired for industrial uses in functional foods.