A novel consortium of Lactobacillus rhamnosus and Streptococcus thermophilus for increased access to functional fermented foods

Abstract

Background: The lactic acid bacterium Lactobacillus rhamnosus GG is the most studied probiotic bacterium with proven health benefits upon oral intake, including the alleviation of diarrhea. The mission of the Yoba for Life foundation is to provide impoverished communities in Africa increased access to Lactobacillus rhamnosus GG under the name Lactobacillus rhamnosus yoba 2012, world's first generic probiotic strain. We have been able to overcome the strain's limitations to grow in food matrices like milk, by formulating a dried starter consortium with Streptococcus thermophilus that enables the propagation of both strains in milk and other food matrices. The affordable seed culture is used by people in resource-poor communities.

Results: We used S. thermophilus C106 as an adjuvant culture for the propagation of L. rhamnosus yoba 2012 in a variety of fermented foods up to concentrations, because of its endogenous proteolytic activity, ability to degrade lactose and other synergistic effects. Subsequently, L. rhamnosus could reach final titers of 1E+09 CFU ml(-1), which is sufficient to comply with the recommended daily dose for probiotics. The specific metabolic interactions between the two strains were derived from the full genome sequences of L. rhamnosus GG and S. thermophilus C106. The piliation of the L. rhamnosus yoba 2012, required for epithelial adhesion and inflammatory signaling in the human host, was stable during growth in milk for two rounds of fermentation. Sachets prepared with the two strains, yoba 2012 and C106, retained viability for at least 2 years.

Conclusions: A stable dried seed culture has been developed which facilitates local and low-cost production of a wide range of fermented foods that subsequently act as delivery vehicles for beneficial bacteria to communities in east Africa.

Figures

Fig. 1

Chromosomal regions of different streptococci genome sequences. aS. thermophilus C106; bS. thermophilus LMD-9; cS. thermophilus JIM8232; dS. thermophilus MN-ZLW-002; eS. thermophilus CNRZ1066 and fS. thermophilus LMG 1831 depicting the genomic island flanked by mobile elements of four open reading frames: potC (truncated), potD, eriC, prtS. Other genes in this figure are coaA (pantothenate kinase), ciaH (sensor protein), fhs (formate-tetrahydrofolate), pgmA (phosphoglucomutase), metF (methylenetetrahydrofolate reductase), metE (5-methyltetrahyropteroltriglutamate-homocysteine S-methyl transferase), pabB (para-amino benzoate synthase component I), pacL1 (Ca2+, Mn2+, P-ATPase)

Fig. 2

Fermentation profile of S. thermophilus C106 in milk at different temperatures. (filled circle) 32 °C; (filled triangle) 37 °C; (filled square) 42 °C; (unfilled square) 45 °C

Fig. 3

Fermentation capacity of seed cultures in pasteurized semi-skimmed milk inoculated after different storage time and at different growth temperatures. 45 °C, 2 years old (filled circle, unfilled circle); 45 °C fresh (filled triangle, unfilled triangle); 37 °C 2 years old (filled square, unfilled square)

Fig. 4

Transmission electron microscopy observations of piliated Lactobacillus rhamnosus strain yoba 2012. Cells were isolated from fermented milk and immuno-gold labeled with anti-SpaA antibodies and gold particule-conjugated protein A. Gold particules (5 nm) co-localize with pilus structures (black dots on pictures)

Fig. 5

Immunoblotting analysis of fermented milk after first (a) and second passage (b) using anti-SpaA serum. Single L. rhamnosus colonies were randomly picked from 2-day old MRS agar plates and analyzed by immunoblotting using anti-SpaA polyclonal antibodies. In a 70 out of 72 colonies tested were pilus positive (97.2 %). In b 101 out of 108 colonies tested were pilus positive (93.5 %). Note: a third immunoblotting (not shown in Fig. 5) was performed for sample 2b and included in the piliation percentage calculation above. Piliation phenotype of some colonies tested was further confirmed by PCR analysis as described in the “Methods”

Fig. 6

Additional benefits of foods fermented with Lactobacillus rhamnosus. a Growth of the pathogen Cronobacter sakazakii in sorghum in presence (unfilled circle) and absence (filled circle) of fermenting Lactobacillus rhamnosus. b Change in vitamin B content of soy after and before fermentation