FIG 4.

Differential impact of natural transformation on the colonization fitness of pneumococcal isolates with diverse transformation capacity. (A) The transformation frequency values of the 18 pneumococcal isolates selected for comparative analysis of the in vivo fitness and virulence traits in the mouse models. The strains in each of three transformability groups are indicated by blue (low), black (intermediate), and red (high) bars. The transformants are presented as the mean CFU ± the standard errors in the presence of selection antibiotic from triplicate samples. The identification and serotype information of each strain are indicated below each bar. NT, nontypeable capsular serotype. (B) The contribution of the transformation to the nasal colonization fitness of the 18 selected pneumococcal isolates with different transformability capacity during the coinfection of each isolate and its ΔcomGC mutant. The competitive index (CI) or CFU ratio between each wild-type (WT) and isogenic mutant (MT) pair was calculated by obtaining nasal washings of the BALB/c mice infected by intranasal inoculation with the 1:1 mixture of the strain pair 4 days earlier. Each symbol represents CI value of a single mouse. The transformability category of each strain is indicated by blue (low), black (intermediate), or red (high) color. The horizontal bars indicate the medians in individual groups of mice. *, P < 0.05; **, P < 0.01; ***, P < 0.001. (C) The colonization levels of the 18 pneumococcal isolates. The total CFU value of the wild-type strain in the output pool from each mouse in the coinfection experiment (described in panel B) is presented as in panel B.