Ability of Vibrio vulnificus to obtain iron from hemoglobin-haptoglobin complexes

It has been suggested that the normal serum protein, haptoglobin (Hp), serves a bacteriostatic role by binding free hemoglobin (Hm), thus making heme iron unavailable for bacterial growth. Previous studies showed that, unlike Escherichia coli, Vibrio vulnificus was able to overcome this Hp-blocking effect. We report here a study on the iron-withholding property of the three major human Hp phenotypes, Hp 1, 2, and 2-1. Results of experiments with human serum showed that V. vulnificus C7184 was able to obtain iron from Hm bound to Hp types 1 and 2, but not that bound to Hp 2-1. E. coli 2395-80, on the other hand, was unable to overcome the blocking effect of any Hp phenotype. Using purified Hp 1, we also demonstrated that, although V. vulnificus was unable to grow in a deferrated medium without an additional iron source, it was able to grow with the addition of the Hm-Hp complex.