In vivo Imaging of a Novel Strain of Bacteroides fragilis via Metabolic Labeling

Non-toxigenic Bacteroides fragilis is regarded as a potential candidate for probiotic owing to its various advantages. We previously isolated a new strain of B. fragilis (ZY-312) and verified its biosafety and capability of inhibiting the growth of pathogens in vivo. However, the colonization of ZY-312 in gastrointestinal (GI) tract remains to be determined. To track the colonization of ZY-312, mice were gavaged with ZY-312 labeled by means of metabolic oligosaccharide engineering and bioorthogonal click chemistry or given AF647-dibenzocyclooctyne (DIBO) directly. Then the fluorescence was detected in GI tract, spleen and kidneys. Results showed that ZY-312 could be labeled by metabolic oligosaccharide engineering, and the optimal incubation time with AF647-DIBO was 5 h in vitro. Following oral gavage with AF647-DIBO labeled ZY-312 or AF647-DIBO alone, mice were subjected to in vivo imaging and the fluorescence intensity was similar in both groups 3 h, 6 h, and 12 h post the gavage. The fluorescence of AF647-DIBO group disappeared 24 h post gavage which was probably due to the excretion via GI tract. While the fluorescence of AF647-DIBO labeled ZY-312 retained in the cecum for as long as 48 h. Immunofluorescence assay further confirmed that labeled ZY-312 transiently colonized not only in cecum but also in stomach, ileum and colon of mice 48 h post-gavage and that no massive accumulation of ZY-312 was detected in other organs such as kidneys and spleen. In conclusion, ZY-312 could transiently colonize in GI tract, mainly in cecum, for at least 48 h, and it hardly disseminate to other organs, which shed new light on the future development of B. fragilis as a probiotic product.