Drug Susceptibility Testing of Anaerobic Protozoa

A simple technique for routine, reproducible global surveillance of the drug susceptibility status of the anaerobic protozoa Trichomonas, Entamoeba, and Giardia is described. Data collected using this technique can be readily compared among different laboratories and with previously reported data. The technique employs a commercially available sachet and bag system to generate a low-oxygen environment and log(2) drug dilutions in microtiter plates, which can be monitored without aerobic exposure, to assay drug-resistant laboratory lines and clinically resistant isolates. MICs (after 2 days) of 3.2 and 25 μM indicated metronidazole-sensitive and highly clinically resistant isolates of T. vaginalis in anaerobic assays, respectively. The aerobic MICs were 25 and >200 μM. MICs (1 day) of 12.5 to 25 μM were found for axenic lines of E. histolytica, and MICs for G. duodenalis (3 days) ranged from 6.3 μM for metronidazole-sensitive isolates to 50 μM for laboratory metronidazole-resistant lines. This technique should encourage more extensive monitoring of drug resistance in these organisms.