Human fecal CLA isomer shifts associated with Bifidobacterium breve MCC1274 and supported by strain-specific in vitro metabolism

Bifidobacteria contribute to host health through diverse microbial metabolites. Among these metabolites, conjugated linoleic acid (CLA) isomers are lipid-derived compounds, and several Bifidobacterium strains have been reported to convert linoleic acid (LA) into CLA. However, it remains unclear whether intake of a human-associated Bifidobacterium strain is associated with fecal CLA isomer profiles in humans and how strain-specific LA conversion contributes to these changes. In this study, we performed a secondary analysis of paired fecal samples collected before and after intake of a test food containing Bifidobacterium breve MCC1274 with lactulose, together with bacterial in vitro culture analyses. Fecal samples from 96 healthy adults were analyzed by targeted LC–MS/MS, shotgun metagenomic sequencing, and strain-specific quantitative PCR. Intake of the test food was associated with shifts in fecal linoleic acid-related metabolite profiles, including significant increases in t9,t11-CLA and t10,c12-CLA. These two CLA isomers were positively correlated with B. breve MCC1274 cell counts. In culture experiments, B. breve MCC1274 produced higher amounts of multiple CLA isomers than B. breve JCM1192 T . RNA sequencing analysis showed that the level of bbi , encoding a BBI-like linoleic acid isomerase, was higher in B. breve MCC1274 than in B. breve JCM1192 T . Further analysis using a bbi mutant indicated that bbi contributes to CLA isomer profiles and linoleic acid-related metabolites. These findings suggest that intake of a test food is associated with shifts in fecal CLA isomer profiles in humans and that strain-specific CLA metabolism of B. breve MCC1274 supports a possible contribution of this strain to these changes.