The influence of iron on Neisseria meningitidis infection in C-57 mice was examined. Iron sulfate, ferric ammonium citrate, and iron sorbitol citrate all proved to be too toxic for use as infection-enhancing agents. Iron dextran displayed an extremely low toxicity, enhanced infection in a dose-dependent manner, and resulted in infection enhancement factors approaching 10(9) for virulent strains of N. meningitidis. Fatal iron dextran-enhanced infection was shown to be reversible by in vivo chelation of iron. Virulent strains of N. meningitidis produced symptoms of infection and pathological lesions in mice both with and without iron pretreatment, but an avirulent strain failed to produce symptoms of infection or pathological lesions, regardless of iron administration. Iron dextran-enhanced infection in mice proved to be a useful model for the examination of virulence of various N. meningitidis strains. All of 9 isolates from clinical disease possessed virulence, whereas only 3 of 10 isolates from carriers possessed virulence, when examined by using this model.

As bstract. The role of iron in experimental infection of mice with Trypanosoma cruzi was investigated. B6 mice had a transient parasitemia and a transient anemia, both of maximal intensity 28 d after the inoculation of T. cruzi. There was a biphasic hypoferremic host response to infection with T. cruzi with the peak hypoferremia also occurring 28 d after inoculation ofthe parasite. The mortality rate from infection was increased from 23% in phosphate-buffered saline-treated B6 mice to 50% in a group of B6 mice receiving iron-dextran (P < 0.025), whereas depletion of iron stores with the iron chelator desferrioxamine B and an iron-deficient diet provided complete protection of B6 mice (P < 0.05). The mortality rate in the highly susceptible C3H strain was reduced from 100% in the control group to 45% (P . 0.025) in the iron-depleted group. The tissue iron stores were altered in mice receiving either iron-dextran or desferrioxamine B and an iron-deficient diet. In vitro, T. cruzi was shown to require both a heme and a nonheme iron source for an optimal growth rate. The effects of iron excess or depletion on the outcome of infection with T. cruzi correlated both with the growth requirements of the parasite for iron and with the availability of intracellular iron. Thus, it was suggested that the hypoferremic response, by sequestering iron within intracellular stores, potentially enhanced the pathogenicity of the intracellular parasites. Furthermore, the in vivo effects of iron excess and depletion correlated with an effect of iron on the growth rate and pathogenicity of the parasite. Dr. Lalonde was also supported by a fellowship from the Medical Research Council of Canada during part of the study period.

DIBI, a purpose-designed hydroxypyridinone-containing iron-chelating antimicrobial polymer was studied for its anti-staphylococcal activities in vitro in comparison to deferiprone, the chemically related, small molecule hydroxypyridinone chelator. The sensitivities of 18 clinical isolates of Staphylococcus aureus from human, canine and bovine infections were determined. DIBI was strongly inhibitory to all isolates, displaying approximately 100-fold more inhibitory activity than deferiprone when compared on their molar iron-binding capacities. Sensitivity to DIBI was similar for both antibiotic-resistant and -sensitive isolates, including hospital- and community-acquired (United States 300) MRSA. DIBI inhibition was primarily bacteriostatic in nature at low concentration and was reversible by addition of Fe. DIBI also exhibited in vivo anti-infective activity in two distinct MRSA ATCC43300 infection and colonization models in mice. In a superficial skin wound infection model, topical application of DIBI provided a dose-dependent suppression of infection along with reduced wound inflammation. Intranasal DIBI reduced staphylococcal burden by >2 log in a MRSA nares carriage model. DIBI was also examined for its influence on antibiotic activities with a reference isolate ATCC6538, typically utilized to assess new antimicrobials. Sub-bacteriostatic concentrations of DIBI resulted in Fe-restricted growth and this physiological condition displayed increased sensitivity to GEN, CIP, and VAN. DIBI did not impair antibiotic activity but rather it enhanced overall killing. Importantly, recovery growth of survivors that typically followed an initial sub-MIC antibiotic killing phase was substantially suppressed by DIBI for each of the antibiotics examined. DIBI has promise for restricting staphylococcal infection on its own, regardless of the isolate’s animal source or antibiotic resistance profile. DIBI also has potential for use in combination with various classes of currently available antibiotics to improve their responses.

Depriving microorganisms of bioavailable iron is a promising strategy for new anti-infective agents. The new, highly water-soluble, low molecular weight co-polymer DIBI was developed to selectively bind iron(iii) ions as a tris chelate and acts as a standalone anti-infective. Minimum inhibitory concentration (MIC) studies show DIBI is effective against representative reference strains for Gram-positive and Gram-negative bacteria and, and the fungus . Compared to the small molecule iron chelators, deferiprone and deferoxamine, DIBI outclassed these by factors of 100 to 1000 for inhibition of initial growth. DIBI and a series of related co-polymers ( of 2-9 kDa) were synthesized reversible addition-fragmentation chain transfer (RAFT) polymerization of a chelating 3-hydroxypyridin-4-one (HPO) methacrylamide monomer and-vinylpyrrolidone (NVP). Full incorporation of the HPO monomer into the co-polymers from the reaction solution was determined by H NMR spectroscopy and ranged from 4.6 to 25.6 mol%. UV-vis spectroscopy showed that all the HPO in DIBI binds readily to iron(iii) in a tris chelate mode to the maximum theoretical iron(iii) binding capacity of the co-polymer. Chemical characterization including single crystal X-ray diffraction analyses of the-benzyl protected and the functional HPO monomer are discussed. By design, DIBI is highly water soluble; the highest mass fraction in water tested was 70% w/w, without the need of organic co-solvents.

Small quantities of iron bound specifically to human transferrin were found to stimulate infection with Neisseria meningitidis strain M1011 in mice. An intraperitoneal injection of 17.5 mg of transferrin carrying 22.7 ytg of Fe resulted in 100% mortality from infection, as compared with no mortality for the controls which had received saline. Five milligrams of ferri-transferrin (FeTf), carrying 6.5 yg of Fe, stimulated and prolonged bacteremia in the mice. Thus, FeTf maintained infection, whereas infection was controlled due to iron limitation in control mice. Comparative studies with apotransferrin (iron-free) revealed that the enhancement of infection was due to the supply of iron. FeTf was also found to relieve an iron limitation of growth achieved by ethylenediaminedihydroxyphenylacetic acid (EDDA) in vitro. FeTf abolished the lag phase for growth of N. meningitidis in a defined medium. The results of this study suggest that human FeTf is an immediate source of iron to N. meningitidis both in vitro and in vivo. These findings support the hypothesis that the levels of iron in the circulating transferrin pool of mice determine the course of experimental N. meningitidis infection.