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JAC Advance Access published online on September 3, 2004
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkh388
© 2004 by The British Society for Antimicrobial Chemotherapy
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Received December 10, 2003
Revised May 21, 2004
Accepted June 29, 2004

Original article

Variability and variation in drug susceptibility among Giardia duodenalis isolates and clones exposed to 5-nitroimidazoles and benzimidazoles in vitro

Raúl Argüello-García 1, Maricela Cruz-Soto 1, Lydia Romero-Montoya 1, and Guadalupe Ortega-Pierres 1*

1 Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados-IPN, Apartado Postal 14-740 07360 México, D.F., México

* To whom correspondence should be addressed. E-mail: gortega{at}mail.cinvestav.mx.


  Abstract

Objectives: We analysed, in a cell-by-cell study, the in vitro susceptibility of Giardia duodenalis strains, including Mexican isolates and their clones to 5-nitroimidazoles and benzimidazoles.

Methods: Fluorogenic dye staining (FDA-PI) and cell morphology (CM) assays, two fast and direct techniques, replaced the indirect ‘gold standard’ method (subculture in liquid medium) in the evaluation of 5-nitroimidazoles and benzimidazoles, respectively.

Results: Under these conditions, the activity of several 5-nitroimidazole and benzimidazole derivatives was consistent with their known efficacy, but parasite stocks exhibited a greater variability in response to 5-nitroimidazoles compared with benzimidazoles. Also, consecutive progenies from single stocks maintained in continuous subculture in drug-free media displayed changes (variations) in the proportions of drug resistant (R/T) subpopulations when exposed to sublethal concentrations of 5-nitroimidazoles and benzimidazoles. These were again more variable upon exposure to 5-nitroimidazoles than to benzimidazoles. Variations were not due to drug susceptibility shifts in parent trophozoites since analysis of cytokinetic processes showed a predominant pattern of susceptible/susceptible or resistant/resistant daughters, whereas susceptible/resistant daughters were scarce.

Conclusions: Our observations support the idea that G. duodenalis cultures exhibit variations in their response to 5-nitroimidazoles and benzimidazoles as a result of a drug-independent competition between drug-susceptible and drug-resistant subpopulations when parasites are subcultured.

Keywords: antiprotozoal drugs; clonal variation; viability assays; cell morphology assays; dye uptake assays.
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