FIGURE 3.

Positive association of vaccine responses with stool Bifidobacterium, B longum, B longum subspecies infantis, and B longum subspecies longum at 15 weeks of age. Infant vaccine responses were characterized as being above (“high”) or below (“low”) the median vaccine responses for the CD4 SI for OPV (A), the CD8 SI for OPV (B), the CD4 SI for PPD as an index of response to the BCG vaccine (C), and for the positive control for polyclonal T-cell proliferation, the CD4 SI for SEB (D). Differences between those above and below the median were identified by the Wilcoxon rank-sum test as indicated by the superscript letters: ^aP < .10, ^bP < .05, ^cP < .01. The Bifidobacterium genus was identified by PCR, B longum species by T-RFLP, and B longum subspecies infantis and B longum subspecies longum as described in Methods.