Mother-to-infant vertical transmission in early life: a systematic review and proportional meta-analysis of Bifidobacterium strain transmissibility

Abstract

Early-life colonization is a critical developmental process influencing infant biological programming, with bifidobacteria playing a key role. This systematic review examines the transmissibility of Bifidobacterium strains from mothers to infants. Adhering to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, 31 articles from 2009 to 2024 were selected from 2825 screened titles and abstracts. Using a narrative synthesis and meta-analysis, the review focuses on studies employing strain-level metagenomic approaches (Protocol registry CRD: CRD42023490507). Ten studies using shotgun metagenomic sequencing identified specific strains of B. adolescentis, B. angulatum, B. bifidum, B. breve, B. pseudocatenulatum, B. catenulatum, and B. longum shared between mothers and infants. A meta-analysis of 810 mother-infant pairs revealed an overall species transmissibility estimate of 30% (95% CI: 0.17; 0.44), with B. longum strains persisting in infants' guts for up to 6 months. Strain transmissibility was higher in vaginally delivered infants compared to those delivered by caesarean section. This review highlights the high transmission rates of maternal Bifidobacterium strains in early-life gut seeding, particularly B. bifidum and B. longum. Despite ongoing research, uncertainties remain regarding the precise characteristics, transmission routes, and mechanisms of transmitted strains. Comprehensive approaches, including metagenomic sequencing and longitudinal studies, are needed to understand the role of vertical transmission in infant gut microbiome engraftment and its functional implications.

E.F.V. acknowledges the assistance provided by the day-to-day discussions in the M.C.C. Lab at the Institute of Agrochemistry and Food Technology (IATA), which facilitated the exploration of the complex concept of Vertical Transmission. E.F.V. thanks to a Predoctoral grant awarded by the Spanish Ministry of Science and Innovation and the European Social Fund Plus (ESF+) for the training of doctors within the framework of the State Plan for Scientific, Technical and Innovation Research 2021–2023 (ref. CEX2021-001189-S-20-1). M.E.T. has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie postdoctoral grant (MicroMI, grant agreement number 898088). M.C.C. acknowledges the support by the European Research Council Starting grant (MAMI grant ref. 639226), Spanish Ministry of Science and Innovation (MAMI-Plus ref. PID2022-139475OB-I00). IATA-CSIC authors also acknowledge the Spanish government MCIN/AEI to the Center of Excellence Accreditation Severo Ochoa (CEX2021-001189-S/MCIN/AEI/10.13039/501100011033). DvS acknowledges Science Foundation Ireland (SFI) support through the Irish Government’s National Development Plan (SFI/12/RC/2273-P1 and SFI/12/RC/2273-P2). L.J.H. is supported by a Wellcome Trust Investigator Award 220876/Z/20/Z and a Biotechnology and Biological Sciences Research Council (BBSRC) Institute Strategic Programme Food, Microbiome and Health BB/X011054/1 and its constituent project BBS/E/F/000PR13631. M.V.C. acknowledges funding from the Spanish Ministry of Science and Innovation (PID2022-139328OA-I00), the Spanish Ministry of Universities (Beatriz Galindo Junior Fellowship BG22/00172), and La Caixa Incoming Junior Leader (LCF/BQ/PI24/12040001).