Figure 3. Capsule heterogeneity among B. fragilis strains contributes to variable host immune responses.

A) Transmission electron microscopy of six representative B. fragilis strains: NCTC 9343, HCBf046, HCBf104, 638R, HCBf077, and HCBf084. Phylogroup and PSA operon (P#/PSA#) are as indicated. Scale bar, 200 nm.

B) Capsule analysis where mole percentage of monosaccharides of six representative B. fragilis strains was determined by GC-MS. Rib, ribose; Rha, rhamnose; Fuc, fucose; Man, mannose; Gal, galactose; Glc, glucose; GalA, galacturonic acid; Hep, heptose; KDO, ketodeoxyoctonic acid; GlcNAc, N-acetylglucosamine; GalNAc, N-acetylgalactosamine.

C) Capsule analysis where fatty acid percentage of six representative B. fragilis strains was determined by GC-MS.

D) O-antigen analysis of whole cell lysates from six representative B. fragilis strains stained using Pro-Q Emerald glycoprotein stain.

E) Serum killing assay of six representative B. fragilis strains. 10⁶ CFU of B. fragilis were treated with 0% or 60% normal human serum (NHS) in 1x PBS for 180 minutes. Results show the percent survival of B. fragilis strains. Two-way ANOVA comparing the mean of B. fragilis strains survival at 0% and 60% NHS. Data are representative of 3 experiments.