In Vitro Susceptibility of Pathogenic Naegleria and Acanthamoeba Species to a Variety of Therapeutic Agents

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Abstract
Six pathogenic strains of Naegleria fowleri , two of Acanthamoeba castellanii , and three of Acanthamoeba polyphaga were tested in vitro for susceptibility to a variety of potentially useful therapeutic agents. Minimal motility inhibitory concentrations and minimal inhibitory concentrations were determined by a technique of subculturing pure clones of amoebae in plastic tissue culture chamber slides containing liquid axenic media and serially diluted drug, incubating at 30°C for Acanthamoeba and at 37°C for Naegleria , and observing on an inverted microscope at 6 h for inhibition of motility and at 24 and 48 h for inhibition of growth. Drug concentrations were selected on the basis of fluid levels achievable in humans. Amphotericin B, clotrimazole, and miconazole were the most effective drugs against Naegleria , whereas polymyxin B sulfate and pentamidine isethionate were somewhat effective against pathogenic Acanthamoeba . Our results suggest that amphotericin B is the most effective agent against Naegleria , but few agents are effective against Acanthamoeba .