ALBENDAZOLE RESISTANCE IN GIARDIA IS CORRELATED WITH CYTOSKELETAL CHANGES BUT NOT WITH A MUTATION AT AMINO-ACID-200 IN BETA-TUBULIN

Albendazole resistance was induced in three different Giardia cultures following growth in successively increasing amounts of drug. One of t he lines was previously resistant to high levels of metronidazole and was able to grow in 2 mu M albendazole. The other two survived exposur e to 0.8 mu M, while normally lethal levels of albendazole against Gia rdia in vitro were around 0.1-0.2 mu M. Albendazole-resistant Giardia were cross-resistant to parbendazole. Major chromosome rearrangements were evident in the line resistant to 2 mu M albendazole and IFA with antitubulin antibody indicated differences in the cytoskeleton, partic ularly the median body, between sensitive and resistant lines. This im plicates the cytoskeleton in the mechanism of resistance. Substitution of Tyr for Phe is a consistent beta-tubulin amino acid change in the benzimidazole-resistant helminths and fungi so far analyzed. PCR prime rs were designed from the published Giardia beta-tubulin gene sequence and spanned the region encoding Phe at position 200. Sequence data fr om albendazole-resistant Giardia demonstrated that the beta-tubulin ge ne did not carry a mutation in the codon for amino acid 200. These dat a suggest that Phe at position 200 in beta-tubulin is not necessary fo r benzimidazole resistance.