Ability of Neisseria gonorrhoeae, Neisseria meningitidis, and commensal Neisseria species to obtain iron from transferrin and iron compounds

Abstract

The ability of Neisseria species to use iron compounds and to compete with iron-binding proteins was examined with deferrated defined medium and the iron chelator deferoxamine. All Neisseria species were able to assimilate a variety of ferric and ferrous iron salts. They were not able to efficiently solubilize an inorganic iron salt such as ferric nitrate, but were able to use iron chelated by citrate, oxalacetate, pyrophosphate, or nitrilotriacetate. Each of the 95 Neisseria isolates examined was able to use hemin as a sole source of iron, and most, but not all, of the isolates were able to obtain iron from hemoglobin. Heated human serum stimulated growth of all gonococci, meningococci, and some commensal Neisseria species in iron-deficient medium. All gonococci and meningococci were able to scavenge iron from 25% saturated transferrin, whereas most commensal organisms were inhibited by this iron-binding protein. The ability to compete with transferrin was specific, since partially saturated conalbumin was bacteriostatic for all Neisseria species. Although the pathogenic Neisseria species were able to compete more efficiently with transferrin for iron than were the nonpathogenic Neisseria species, no correlation was observed between the virulence of different strains or colony types of gonococci and the ability to scavenge iron in vitro from transferrin or other chelators.

Mechanisms of iron acquisition and bacterial virulence

“…As in the case of Neisser~a meningitidis, both the receptors for transferrin and iactoferrin from Netsseria gonorrhoeae, are specific for the human proteins [151}, but the role of this system for iron acquisition on the virulent properties of gonococci has been established in neither case. It is also well known that Neisseria 8onorrhoeae can grow using haemoglobin as the sole source of iron [145,152]. These data are important, since haemoglobin is freely available on vaginal mucosa during menses, a circumstance that can contribute to better growing of gonococci in this habitat.…”

“…it has been shown that the availability of iron influences the virulent properties of Neisseria meningitidis [139][140][141]. Although Neisseria seems not to produce siderophores |142-144], Neisseria meningttidJs might acquire iron from transferrin [143][144][145] and iactofcrrin [146] through specific membrane receptors [147,148]. The receptor for transferrin is iron regulated, and seems to be highly specific for human transferrin [1471.…”

“…This indicates that the acquisition of iron from transferrin is important for the complete expression of the virulent properties of the microorganism. In the case of Neisseria gonorrhoeae, it has also been shown that this microorganism is unable to synthesize siderophores [41349] and can acquire iron from lactoferrin or transferrin [41, 145,146]. The suggested mechanism implies the binding of iron-transferrin to a membrane receptor, internalization of the metal (not the transferrin) and binding of transferrin to another molecule of iron [41].…”

Identification and characterization of a high-affinity zinc uptake system in Neisseria gonorrhoeae

“…Many bacterial ABC transporters are virulence factors that enhance the ability of the organism to grow or survive in a variety of environments [21]. For example, the presence of the FbpABC transporter in N. gonorrhoeae is required for the acquisition of iron from TF or LF [22], and, therefore, is able to colonize and cause disease in humans [23]. Evidence to substantiate that bacterial ZnuABC transporters are important in virulence is limited.…”

The effect of iron on the metabolism and pathogenicity of Neisseria gonorrhoeae

“…Irrespective of whether or not gonococci produce siderophores, there is, nevertheless, convincing evidence that gonococci can obtain iron from both transferrin and lactoferrin, the ironbinding glycoproteins found in host tissues. All strains of gonococci tested have been shown to scavenge iron from 25% saturated transferrin, whereas most strains of commensal Neisseria organisms lack this ability [6]. By way of contrast, 53% of gonoccal strains and 24% of commensal Neisseria strains tested could use lactoferrin-bound iron [7].…”