Growth of H. influenzae strains with free heme as the sole heme source. Growth of the H. influenzae strain Rd KW20 and the dppC insertion mutant strain TMV1262 in hdBHI supplemented with heme as the sole heme source. Wildtype strain Rd KW20 at 10 μg ml-1 heme (solid circles), at 2 μg ml-1(solid triangles) and at 1.25 μg ml-1 (solid squares). The dppC insertion mutant strain TMV1262 at 10 μg ml-1 heme (open circles), at 2 μg ml-1 (open triangles) and at 1.25 μg ml-1 (open squares). Results are mean ± SD for quintuplicate results from representative experiments. The Kruskal-Wallis test was used to compare growth of Rd KW20 and TMV1262 over the entire 24 hour growth period at all heme concentrations (P < 0.0001 for all comparisons).