TF and infection: However, Zhao et al. [55] noted growth of wild-type meningococcal strains on 30–50 μg/ml free Hb and so it is not clear if the availability of free Hb was a determinant of the inability of tbp mutants to replicate in whole blood, The discrepancy may arise from the fact that the whole blood model only mimics the early stages of an infection where iron-loaded Tf is abundant [56, 57].