4.6 Article

Safety Evaluation of a Novel Strain of Bacteroides fragilis

Journal

FRONTIERS IN MICROBIOLOGY
Volume 8, Issue -, Pages -

Publisher

FRONTIERS MEDIA SA
DOI: 10.3389/fmicb.2017.00435

Keywords

Bacteroides fragilis; safety evaluation; probiotic; whole genome sequencing; genetic stability

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Funding

  1. National High Technology Research and Development Program 863 [2015AA020702]
  2. Science and Technology Program of Guangdong, China [2015A010101345, 2016B090918064, 2016A020217010]

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Commensal non-toxigenic Bacteroides fragilis confers powerful health benefits to the host, and has recently been identified as a promising probiotic candidate. We previously isolated B. fragilis strain ZY-312 and identified it as a novel strain based on 16S rRNA sequencing and morphological analyses. We also determined that ZY312 displayed desirable probiotic properties, including tolerance to simulated digestive fluid, adherence, and in vitro safety. In this study, we aim to investigate whether ZY312 meets the safety criteria required for probiotic bacteria through comprehensive and systematic evaluation. Consequently, the fatty acid profile, metabolite production, and biochemical activity of strain ZY-312 were found to closely resemble descriptions of B. fragilis in Bergey's manual. Taxonomic identification of strain ZY-312 based on whole genome sequencing indicated that ZY-312 and ATCC 25285 showed 99.99% similarity. The 33 putative virulence-associated factors identified in ZY-312 mainly encoded structural proteins and proteins with physiological activity, while the lack of bft indicated that ZY-312 was non-toxigenic. In vivo safety was proven in both normal and immune-deficient mice. The 11 identified antibiotic resistance genes were located on the chromosome rather than on a plasmid, ruling out the risk of plasmid-mediated transfer of antibiotic resistance. In vitro, ZY-312 showed resistance to cefepime, kanamycin, and streptomycin. Finally, and notably, ZY-312 exhibited high genetic stability after 100 passages in vitro. This study supplements the foundation work on the safety evaluation of ZY-312, and contributes to the development of the first probiotic representative from the dominant Bacteroidetes phylum.

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