FIG. 2.

Growth of B. pertussis strains cocultured in vitro under various nutritional iron conditions. (A) Growth of strains UT25Sm1 (filled symbols) and heme utilization mutant PM5 (open symbols) cocultured over a 72-h period in iron-replete SS (circles and solid lines), iron-depleted SS (squares and dashed lines), and iron-depleted SS supplemented with 10 μM bovine hemin chloride (triangles and dotted lines). Mean CFU/ml (n = 3) of each strain, represented as the fraction of input CFU, is plotted as a function of time (h). (B) Competitive index values calculated from mean CFU/ml of cocultured strains sampled at various times. Circles, iron-replete SS; squares, iron-depleted SS; triangles, iron-depleted SS with hemin supplementation. The dashed line at a y value of 1.00 corresponds to the hypothesized CI if there were no difference in fitness between the strains cocultured under the specified growth conditions.