HAEMONCHUS-CONTORTUS - THE ROLE OF 2 BETA-TUBULIN GENE SUBFAMILIES INTHE RESISTANCE TO BENZIMIDAZOLE ANTHELMINTICS

The role of beta-tubulin genes in benzimidazole (BZ) resistance was in vestigated using one susceptible (S) and two resistant (Rt and Rc) str ains of Haemonchus contortus. The Rt strain was isolated from the fiel d on the basis of thiabendazole resistance. The Rc strain was derived from the S strain by treatment with cambendazole. cDNAs, derived from the S strain, encoding two isoforms of beta-tubulin (beta 12-16 and be ta 8-9), alpha-tubulin and phosphofructokinase (Pfk) were used as prob es for Southern hybridization analysis of genomic DNA digested by rest riction enzymes. Genomic DNA was isolated from a pool of worms or sing le worms. The restriction-enzyme fragment length polymorphism (RFLP) d ifferences among these strains depended on the enzyme and the probe us ed. When digested with Stu I or Hpa I, and probed under stringent cond itions with beta 8-9 or beta 12-16, fewer fragments were seen in the R t and Rc strains than in the S strain. Different hybridizing fragments were found in different individuals. The frequency of individuals bea ring certain fragments hybridizing to beta 12-16 or beta 8-9 in the su sceptible population was reduced significantly in the resistant popula tions. Some differences in RFLP between these strains were observed wh en probed with alpha-tubulin or Pfk, but the changes were not consiste nt with fragments being lost from the resistant strains as observed fo r beta-tubulin probes. These changes in RFLP pattern correlate with ch anges in the binding profiles of BZs and isoelectric isoform patterns reported previously for these strains. The data confirm that reduced h eterogeneity within the population is associated with BZ resistance. O ur results show that both the beta 8-9 and the beta 12-16 subfamilies of beta-tubulin are affected to a similar extent by this reduction in heterogeneity in a resistant population.