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Oct 28 11 9:33 PM

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In Vitro Susceptibility Testing of Dientamoeba fragilis

, , , , and 1 Division of Microbiology, SydPath, St. Vincent's Hospital, Darlinghurst, Australia, 2 University of Technology Sydney, Department of Medical and Molecular Biosciences, Broadway, Australia, 3 University of Technology Sydney, iThree Institute, Broadway, Australia ABSTRACT Dientamoeba fragilis is a commonly encountered trichomonad which has been implicated as a cause of gastrointestinal disease in humans. Despite the frequency of reports recording infections with this parasite little research has been undertaken in terms of antimicrobial susceptibility. The aim of this study was to evaluate the susceptibility of D. fragilis to several commonly used anti-parasitic agents: diloxanide furoate, furazolidone, iodoquinol, metronidazole, nitazoxanide, ornidazole, paromomycin, secnidazole, ronidazole, tetracycline and tinidazole. Antibiotic susceptibility testing was performed on four clinical strains of D. fragilis, designated A, E, M and V, respectively. Molecular testing followed and all strains were determined to be genotype 1. Anti-protozoal compounds at concentrations ranging from 2μg/mL to 500μg/mL, were determined via cell counts of D. fragilis trophozoites grown in dixenic culture. Minimum lethal concentrations (MLCs) were ornidazole 8-16μg/mL; ronidazole 8-16μg/mL; tinidazole 31μg/mL; metronidazole 31μg/mL; secnidazole 31-63μg/mL; nitazoxanide 63μg/mL; tetracycline 250μg/mL; furazolidone 250-500μg/mL; iodoquinol 500μg/mL; paromomycin 500μg/mL and diloxanide furoate >500μg/mL. This is the first study to report susceptibility profiles on clinical isolates of D. fragilis to a wide range of commonly used treatments. Our study indicated 5-nitroimidazole derivatives to be the most active compounds in vitro against D. fragilis.