Comparison of relative levels of gut microbiota in secretor-fed infants and non-secretor-fed infants. Asterisks indicate significant differences (p < 0.05) in the relative levels of various gut microbes using a Wilcoxon rank sum test. The color boxplots show the quartiles above and below the median; the dark line near the center of the box denotes the median. The whiskers extend to the first and fourth quartiles, and the black dots show outliers. N = non-secretor, S = secretor.