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

Abstract

Six pathogenic strains ofNaegleria fowleri, two ofAcanthamoeba castellanii, and three ofAcanthamoeba 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 3000 forAcanthamoeba and at 3700 forNaegleria, 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 pathogenicAcanthamoeba. Our results suggest that amphotericin B is the most effective agent against Naegleria, but few agents are effective against Acanthamoeba.

In Vitro Susceptibilities of Naegleria fowleri Strain HB-1 to Selected Antimicrobial Agents, Singly and in Combination

“…There was no indication ofsynergy when AMB was combined with miconazole or when the methyl ester of AMB was combined with either minocycline, tetracycline, or miconazole. DISCUSSION AMB (5,8,9,17), tetracycline (19), rifampin (19), clotrimazole (9,12), and miconazole (9,21) have all shown activity against Naegleria spp. The majority of the assays of these reagents have been carried out either on agar plates or in axenic media, both with and without bacteria as an added nutrient.…”

“…Antiamoebic effects of drugs that have been previously noted include inhibition of growth (5,8,9), inhibition of amoebic motility (5,8,9), and cytotoxic changes observed by light or electron microscopy (17). Definitions of the MIC of a drug have varied in previous studies (5,8,9).…”

“…Definitions of the MIC of a drug have varied in previous studies (5,8,9). Minimal motility inhibitory concentration has been generally defined as light microscopic evidence of trophozoite immobilization (5,8,9 (4) in their study of AMB and rifampin defined synergy as a greater rate and extent of killing with the drugs in combination than with either drug tested alone at a twofold increase in concentration.…”

“…Many different antimicrobial agents (and treatment regimens) have been used to treat PAM, but the most promising appears to be the antifungal polyene, AMB. Both in vitro amoebicidal activity (5,8,9,17) …”

Activities of Azithromycin and Amphotericin B against Naegleria fowleri In Vitro and in a Mouse Model of Primary Amebic Meningoencephalitis

“…Since primary amebic meningoencephalitis was identified, a wide range of therapeutic agents against N. fowleri have been evaluated, including many antifungal, antiprotozoal, antibacterial, and antipsychotic agents. Most of these drugs were determined to have little or no efficacy against N. fowleri, either in vitro or in vivo (5)(6)(7)(8)22).Of the drugs that have been evaluated against N. fowleri, amphotericin B, an antifungal drug, is the only agent with established clinical efficacy. Studies have demonstrated the in vitro and in vivo activity of amphotericin B against various strains of N. fowleri (5-8, 13, 17, 19, 20, 21), and at least seven patients with primary amebic meningoencephalitis have been successfully treated with amphotericin B alone or in combination with other drugs (1,2,14,16,19,25).…”