Iron Utilization and Invasiveness of Hemophilus influenzae
Hemophilus influenzae classically has been defined as a heme-requiring microorganism. Many species of microorganisms use heme in vitro, but there probably is not very much unbound heme available in vivo. It is known that free heme is bound in the serum to hemopexin and is rapidly removed to an intracellular location. Free hemoglobin is similarly bound to haptoglobin and rapidly removed from serum. The most abundant (and most persistent) iron source in serum is iron-transferrin. The question investigated was, can a microbe that by definition requires heme for growth in vitro actually use other iron sources such as transferrin that might be more readily available in vivo?