Mechanism of Tuberculostasis in Mammalian Serum II. Induction of Serum Tuberculostasis in Guinea Pigs

Abstract

The growth of tubercle bacilli in serum samples of untreated animals depends upon the availability of ionic iron which serves as a growth factor in supporting bacillary multiplication. The amount of available iron in serum is determined by the ratio between iron-saturated and iron-free transferrin; a low value for the ratio is associated with tuberculostasis (e.g., human serum, 0.4), whereas a high value is associated with the growth-supporting quality (e.g., guinea pig serum, 5.6). The treatment of guinea pigs with lipopolysaccharide of Escherichia coli or tuberculous cell wall material consistently and significantly reduced serum iron levels; a similar but less striking effect was observed in BCG-vaccinated animals. Pronounced differences were observed in the time of appearance and duration of serum hypoferremia; in lipopolysaccharide-treated animals, it appeared in 1 day and lasted for several days, whereas in BCG-vaccinated animals it appeared in about 2 weeks and lasted for much longer time periods. The induced hypoferremia was always associated with the concomitant development of serum tuberculostasis which could be neutralized by the addition of iron. These results indicate, therefore, that the mechanism of induced serum tuberculostasis in lipopolysaccharide- or tuberculous cell wall-treated and BCG-vaccinated guinea pigs is the same as that present in tuberculostatic sera of untreated animals.

Detection and differentiation of iron-responsive avirulent mutants on Congo red agar

“…This increased virulence in the presence of iron is accompanied by an enhancement of growth in vivo to a level approximating that of P+ strains. Iron has been shown to influence virulence of a variety of other microorganisms including Escherichia coli (1,12), Pseudomonas aeruginosa (2), and Mycobacterium tuberculosis (11).…”

Mechanism of Tuberculostasis in Mammalian Serum III. Neutralization of Serum Tuberculostasis by Mycobactin

“…Previous studies (6,7) disclosed that tubercle bacilli cannot grow in mammalian sera because the sera fail to provide the parasites with growthessential iron. Results showed that a serum can support bacillary growth only when sufficient iron is provided to saturate the iron-binding protein transferrin (Tr) to a point at which unbound iron is available for bacillary utilization.…”

“…Determination of the iron content in 1 ml of this medium showed that it contained 0.16 ,sg of the metal. This amount of iron saturates Tr in the medium to 80% at which point there is enough unbound iron to initiate bacillary growth (7).…”

“…Neutralization of serum tuberculostasis. The detailed description of techniques employed in demonstration of serum tuberculostasis and in the neutralization of the tuberculostasis with iron has been provided in previous communications (6)(7)(8)(9). The neutralization of serum tuberculostasis was performed in screw-capped tubes in which various dilutions of spent medium or mycobactin weie added to tuberculostatic bovine serum.…”

Role of Mycobactin in the Growth and Virulence of Tubercle Bacilli

“…The investigation of the role of M in the neutralization of serum tuberculostasis revealed that M does not serve as a growth factor but as a carrier of growth-essential iron which M removes from transferrin (Tr) and provides to tubercle bacilli in a utilizable form (15). The role of M in the development of tuberculosis can be limited by BCG and lipopolysaccharide treatments which induce hypoferremia and increase the degree of serum tuberculostasis in treated animals (14). The consideration of induced hypoferremia led to the development of nutritional immunity concept which may play a major role in the host-parasite relationships (11).…”