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Microbiology 150 (2004), 1231-1236; DOI  10.1099/mic.0.26836-0
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Microbiology 150 (2004), 1231-1236; DOI  10.1099/mic.0.26836-0
© 2004 Society for General Microbiology

Menadione kills trophozoites and cysts of Giardia intestinalis

Timothy Paget1, Sarah Maroulis2, Andrew Mitchell2, Michael R. Edwards2, Edward L. Jarroll3 and David Lloyd4

1 Department of Applied Biology, University of Hull, UK
2 School of Biotechnology and Bio-molecular Sciences, University of New South Wales, Sydney, Australia
3 Department of Biology, Northeastern University, Boston, MA 02115, USA
4 Microbiology Group (BIOSI 1, Main Building), Cardiff University, PO Box 915, Cardiff CF10 3TL, UK

Correspondence
David Lloyd
Lloydd{at}cf.ac.uk

Production of reactive oxygen species by redox cycling in the presence of low levels of oxygen has been studied as a possible approach to anti-protozoal chemotherapeutic strategy. Incubation of the diplomonad flagellate Giardia intestinalis with 2-methy-1,4-naphthoquinone (menadione), under anaerobic conditions, gave UV absorption changes characteristic of reduction to menadiol; partial reversal was observed on admitting O2. Under microaerobic conditions, similar to those on the surface of the jejunal mucosa, trophozoites consumed O2 rapidly in the presence of menadione; reaction products included singlet O2 (monitored by single photon counting of O2-dependent low-level chemiluminescence) and H2O2 (measured by the formation of Complex I of microperoxidase). Trophozoites became swollen and incapable of regulatory volume control; these irreversible responses led to loss of motility, cessation of flagellar activity and cell death. Comparison of the sensitivities of trophozoites to metronidazole and menadione gave LC50 values (µg ml–1) of 1·2 and 0·7, respectively; corresponding values for cysts (measured by in vitro excystation capacities) were >50 and 1·3. Menadione (LD50 in mice, 0·5 g kg–1) is therefore a potentially more useful and general anti-giardial agent than metronidazole, as it is active against cysts as well as trophozoites.

Abbreviations: ESR, electron spin resonance; ROS, reactive oxygen species






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