Possible roles for pyruvate: Ferredoxin oxidoreductase and thiol-dependent peroxidase and reductase activities in resistance to nitroheterocyclic drugs in Giardia intestinalis

Giardia intestinalis was found to lack glutathione, though it did possess abundant quantities of unidentified thiol(s) as well as thioldependent peroxidase and reductase activities. These activities were positively correlated in 14 isolates with in vitro resistance to furazolidone, but not metronidazole or tinidazole. The resistance of 17 isolates to metronidazole was, however, negatively correlated with pyruvate: ferredoxin oxidoreductase activity as was drug resistance in a line of G. intestinalis selected for resistance to metronidazole. This suggests different modes of action for nitrofurans and 5-nitroimidazoles.