Albendazole Resistance in Giardia Is Correlated with Cytoskeletal Changes but Not with a Mutation at Amino Acid 200 in β-Tubulin

ABSTRACT

Albendazole resistance was induced in three different Giardia cultures following growth in successively increasing amounts of drug. One of the lines was previously resistant to high levels of metronidazole and was able to grow in 2 μM albendazole. The other two survived exposure to 0.8 μM, while normally lethal levels of albendazole against Giardia in vitro were around 0.1–0.2 μM. Albendazole-resistant Giardia were cross-resistant to parbendazole. Major chromosome rearrangements were evident in the line resistant to 2 μM albendazole and IFA with antitubulin antibody indicated differences in the cytoskeleton, particularly the median body, between sensitive and resistant lines. This implicates the cytoskeleton in the mechanism of resistance. Substitution of Tyr for Phe is a consistent β-tubulin amino acid change in the benzimidazole-resistant helminths and fungi so far analyzed. PCR primers were designed from the published Giardia β-tubulin gene sequence and spanned the region encoding Phe at position 200. Sequence data from albendazole-resistant Giardia demonstrated that the β-tubulin gene did not carry a mutation in the codon for amino acid 200. These data suggest that Phe at position 200 in β-tubulin is not necessary for benzimidazole resistance.