Oral live microbial therapeutics: A synthetic biology roadmap toward durable oral microbiome-based therapies

Oral live microbial therapeutics (LMTs) show promise for halitosis, caries, and adjunctive periodontal care, yet benefits often fade after dosing stops. We synthesized evidence across indications and reframed development around quantifying and engineering persistence at intraoral sites, while outlining safety-by-design and delivery considerations for the oral niche.

This narrative review integrated randomized trials, observational studies, and in vitro/ex vivo investigations to characterize clinical outcomes, persistence-related metrics, and engineering principles relevant to oral LMT development. Sources included PubMed/MEDLINE, Web of Science, Embase, and ClinicalTrials.gov, with backward/forward citation tracking. We included studies on LMTs in oral or gut contexts when mechanistically informative for oral applications (e.g., persistence, delivery, or biocontainment). Eligibility required clinical outcomes or persistence-related readouts. Two reviewers screened records and resolved disagreements by consensus. Reporting and assay principles were informed by STORMS and MIQE to support transparent, reproducible methods.

Across indications, effects typically peak during dosing and attenuate after cessation, varying with strain, delivery format, and co-interventions (e.g., tongue dorsum debridement; standardized periodontal care). Persistence is rarely co-measured with clinical endpoints, limiting mechanistic interpretation. We outline a site-resolved measurement set, including time above the limit-of-detection, colonization area under the curve, apparent half-life (t½), and t½ under oral-mimetic shear, together with an engineering toolkit combining mucoadhesive/enamel-interactive carriers, single-cell coatings, and multilayer biocontainment (e.g., logic-gated/CRISPR kill switches, synthetic auxotrophy), and chemistry, manufacturing, and controls considerations.

Embedding persistence metrics and safety-by-design into study protocols may support more durable outcomes, and standardized, site-resolved reporting will be essential for clinical translation.