INVOLVEMENT OF SUPEROXIDE-DISMUTASE AND PYRUVATE-FERREDOXIN OXIDOREDUCTASE IN MECHANISMS OF METRONIDAZOLE RESISTANCE IN ENTAMOEBA-HISTOLYTICA

Metronidazole resistance has been induced in an axenic strain of Entam oeba histolytica (HTH-56:MUTM) following continuous exposure to steadi ly increasing drug concentrations. The drug-resistant line is routinel y maintained in normally lethal levels of metronidazole (10 mu M). Res istance to this concentration of drug was developed over 177 days. Dec reased pyruvate:ferredoxin oxidoreductase (PFOR) activity in anaerobic organisms is one mechanism of metronidazole resistance but in entamoe ba, PFOR activity was not decreased in metronidazole-resistant parasit es as determined by immunofluorescent assays and immunoblotting studie s. 2-Oxoacid oxidoreductase activity, which appeared to be due to a si ngle enzyme, PFOR, was evident with pyruvate as well as the alternativ e substrates, alpha-ketobutyrate, alpha-ketoglutarate and oxaloacetate . A marked increase in superoxide dismutase (SOD) activity was detecte d in metronidazole-resistant E. histolytica. Increased SOD activity ha s not previously been documented as a mechanism of drug resistance alt hough SOD has been associated with a range of stress situations in oth er organisms.