The viability and persistence of orally administered microbes in the human gut are essential to their biological function. We previously described the development of two synbiotic medical foods, SBD111 and SBD121, each comprising four food-derived microbial strains and prebiotic fibers for the dietary management of postmenopausal bone loss and rheumatoid arthritis, respectively. Here, we report a randomised, open-label clinical study examining the persistence of SBD111 and SBD121 microbes in faecal samples from healthy adults following administration for seven days. Thirty-eight participants, aged 18-64 years with BMI 18.5-35 kg/m2, were randomised to receive one of the two synbiotic medical foods daily for one week, followed by a four-week monitoring period. Employing quantitative PCR (qPCR), shotgun metagenomics, and culture-based assays, we evaluated the presence and viability of the microbial strains comprising each synbiotic medical food during and after administration. SBD111 and SBD121 were well-tolerated with minimal adverse events reported. Strains were detected in over 80% of participants during the administration period, with strain abundance peaking in the first week. Persistence in the follow-up period varied by strain and detection method. The microbial strains were detected by qPCR and metagenomic sequencing for a median of seven days and three days during the follow-up period, respectively. However, Bacillus amyloliquefaciens was consistently detected for seven days by both methods. Culture-based assays confirmed the presence of viable strains from both synbiotic medical foods in stool samples up to one-week post-consumption. Faecal metagenome diversity and metabolic functional potential remained stable throughout the administration and follow-up periods, aligning with previous findings in healthy adults. Collectively, these results establish that SBD111 and SBD121 deliver viable microbes that transiently persist in the gut, reinforcing their promise for safe and targeted dietary interventions.

This trial is registered at ClinicalTrials.gov (NCT06614166) and was funded by Solarea Bio Inc.

KJM, IMW, LAMdOV, MJSG, EMS, MRC, AEB, GVT are employed by Solarea Bio, Inc. SJ served as clinical monitor of the clinical study and was paid a consulting fee.

NCT06614166

This study was funded by Solarea Bio Inc.

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Ethics committee/IRB of Advarra, Inc. gave ethical approval for this work

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The data presented in this study are available on request from the corresponding author.