FIG 1.

Role of Spn serotypes in facilitating competition during colonization. (A) Density of the strain of Spn indicated cultured from URT lavages at 3 days following IN inoculation of 4-day-old pups. Median values are indicated, with each symbol representing a single pup. No significant differences in colonization levels between strains were found when using a Kruskal-Wallis test, followed by Dunn’s multiple comparison test. (B) The roles of serotype, genetic background, and colonization duration on competitive interactions between strains. Pups were each challenged as described above with an even mixture of the strains indicated, and URT lavages were collected at the time point indicated to determine bacterial density with strains distinguished by colony immunoblotting using serotype-specific typing sera. A competitive index was calculated by comparing the ratio of the two strains cultured in URT lavages to the ratio in the inoculum. A competitive index greater than 1 indicates a higher proportion of the serotype 23F compared to serotype 4 strain. Competitive index values of 1,000 were used for pups where only the serotype 23F strain was detected. Median values are indicated, and each symbol represents the competitive index from a single pup. Competitive indices were compared to a hypothetical median of 1, the value representing no competition, using the Wilcoxon Signed Rank test. *, P < 0.05; ns, not significant.