BETA-TUBULIN GENE POLYMORPHISM AND BENZIMIDAZOLE RESISTANCE IN TRICHOSTRONGYLUS-COLUBRIFORMIS

The complement of beta-tubulin alleles in Trichostrongylus colubriform is populations was examined and found to undergo changes similar to th ose previously reported for Haemonchus contortus following selection f or benzimidazole (BZ) resistance. Genomic DNA from BZ-resistant and -s usceptible strains was probed with a series of overlapping fragments d erived from a T. colubriformis beta-tubulin gene. A susceptible popula tion showed a high level of polymorphism (detected as RFLPs with sever al enzymes and directly by sequence analysis) at a locus, tcb-1, which appears to be the homologue of the gru-1 locus in H. contortus. This polymorphism disappeared following selection for BZ resistance, leavin g a single tcb-1 allele in the resistant population. The same single a llele was present in 2 additional, unrelated resistant populations. Th ese data support the hypotheses that tcb-1 and gru-1 are major determi nants of BZ susceptibility and hence a major target of BZ-resistance s election.