Certain drugs that interfere with folate metabolism (sulfones, sulfonamides, and inhibitors of dihydrofolate reductase) play an important role in the chemotherapy and prophylaxis of malaria. The activities and mechanisms of action of these drugs are regarded as similar in most respects to their activities against procaryotic microorganisms. Believed incapable of utilizing intact exogenous folates, plasmodia have been regarded as dependent on de novo synthesis of required folate cofactors. The present investigation, conducted in pursuit of a method for testing the in vitro susceptibility of Plasmodium falciparum to antifol antimalarial drugs, produced evidence that earlier assumptions about the folate metabolism of this organism are not correct. Three of four isolates of P. falciparum were successfully maintained in a culture medium depleted of folic acid and p-aminobenzoic acid. The antimalarial activities of sulfonamides and dihydrofolate reductase inhibitors were, furthermore, variably antagonized by the presence of folic acid and p-aminobenzoic acid in the culture medium. Optimum conditions for assessment of antifol antimalarial activity in vitro therefore require precise control of these factors in the culture medium. Our results suggest that resistance to antifol antimalarial drugs involves a complex of factors related to both the de novo synthesis of active folate cofactors and the ability to utilize exogenous intact folates in various forms.
The aerotolerance of the microaerophilic bacterium Spirillum volutans was greatly stimulated in a defined medium by the presence of dihydroxyphenyl ferric iron-binding compounds such as nor-epinephrine at 10-5 to 10-6 M. Dihydroxyphenyl compounds at 2 x 10-4 M, or iron salts (ferrous or ferric) at high concentration, greatly increased the aerotolerance of a strain of Campylobacter fetus subsp. jejuni when grown on streak plates of Brucella agar. The results suggest that the microaerophilism of these organisms might in part be caused by a failure to synthesize microbial ferric iron-binding compounds at sufficient levels to support aerobic growth.
Vibrio vulnificus (lactose-positive Vibrio), a recently recognized pathogenic marine species, produced extreme hemoconcentration and death within 3 to 6 h after subcutaneous or intraperitoneal injection of 10(8) viable cells into mice; hemotocrit values approached 70% (normal, 45%). About 1 ml of edema fluid accumulated at the site of each subcutaneous injection, and locally increased vascular permeability was demonstrated by a skin bluing assay, using Evans blue dye. A corresponding fluid accumulation did not occur in the peritoneal cavity after an intraperitoneal injection. Filter-sterilized supernatants of cultures grown under a variety of conditions did not produce local edema or lethality, nor did whole Vibrio cells killed by a variety of methods or disrupted by sonic oscillation. Edema fluids collected from infected mice and sterilized by filtration had no effect when they were injected subcutaneously or intraperitoneally into mice. Inocula of 10(9) viable cells of V. vulnificus contained within a diffusion chamber implanted subcutaneously did not produce skin bluing, edema, or lethality; Vibrio cells remained viable and virulent within these chambers for at least 2 weeks. These experiments suggested that vascular permeability changes in V. vulnificus infections may not be attributable to a diffusible toxin and may require direct contact between host cells and viable Vibrio cells.
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