Studies have identified abnormalities in the microbiota of patients with arthritis. To evaluate the pathogenicity of human microbiota, we performed fecal microbial transplantation from children with spondyloarthritis and controls to germ-free KRN/B6xNOD mice. Ankle swelling was equivalent in those that received patient vs. control microbiota. Principal coordinates analysis revealed incomplete uptake of the human microbiota with over-representation of two genera (Bacteroides and Akkermansia) among the transplanted mice. The microbiota predicted the extent of ankle swelling (R2 = 0.185, p = 0.018). The abundances of Bacteroides (r = −0.510, p = 0.010) inversely and Akkermansia (r = 0.367, p = 0.078) directly correlated with ankle swelling. Addition of Akkermansia muciniphila to Altered Schaedler’s Flora (ASF) resulted in small but statistically significant increased ankle swelling as compared to mice that received ASF alone (4.0 mm, 3.9–4.1 vs. 3.9 mm, IQR 3.6–4.0, p = 0.041), as did addition of A. muciniphila cultures to transplanted human microbiota as compared to mice that received transplanted human microbiota alone (4.5 mm, IQR 4.3–5.5 vs. 4.1 mm, IQR 3.9–4.3, p = 0.019). This study supports previous findings of an association between A. muciniphila and arthritis.