Methods:  K/BxN mice were maintained under germ-free (GF) conditions and were gavaged with feces previously collected from children with ERA and healthy controls at 6 – 10 weeks of age, and maintained in isolators for 21 – 24 days following FMT. Additional controls included non-gavaged GF mice and mice transferred from the gnotobiotic to the conventional facility. Subsequent studies involved colonization with select cultured bacteria. Sequencing of the fecal microbiota was performed on the Illumina MiSeq device, and analysis was performed with the Quantitative Insight into Microbial Ecology program.

Results:  24 mice were gavaged with human microbiota (12 each of ERA and controls). 23 non-gavaged mice were maintained in the gnotobiotic facility, and 11 additional non-gavaged mice were transferred into the conventional facility. Among transplanted mice, ankle swelling assessed 21 – 24 days post transfer was equivalent in those that received ERA (4.7 ± 0.5) vs control (4.4 ± 0.4) microbiota. Taken together, mice colonized with human microbiota had increased ankle swelling as compared to GF (3.5 ± 0.3, p < 0.001) and conventionally housed (4.0 ± 0.4, p = 0.002) mice. Principal coordinates analysis revealed incomplete uptake of the human microbiota, with clustering by species but not by donor-recipient dyad. This was due to substantial over-representation of two genera (Bacteroides and Akkermansia) at the expense of the Firmicutes phylum among the transplanted mice. Taken together, the microbiota as a whole predicted the extent of ankle swelling (R2 = 0.185, p = 0.018, adonis test). At the level of the individual genera, the abundances of Bacteroides (r = -0.510, p = 0.010) inversely and Akkermansia (r = 0.367, p = 0.078) directly correlated with ankle swelling. Although monocolonization of A. muciniphila did not impact ankle swelling, addition of A. muciniphila cultures to transplanted human microbiota resulted in increased ankle swelling as compared to mice that received transplanted human microbiota alone (median 4.5 mm, IQR 4.3 – 5.5 versus 4.1 mm, IQR 3.9 – 4.3, p = 0.018).

Conclusion:  This study supports previous findings of a possible association between Akkermansia muciniphila and arthritis and opens up new avenues of research into the association between human microbiota and arthritis.