The presence of a new SNP at codon 198 of the beta tubulin gene is associated with benzimidazole resistance in Teladorsagia circumcincta

Abstract

In the present study we analyzed the level of resistance to benzimidazoles by the detection of Single Nucleotide Polymorphisms (SNPs) at codons 198 (E198A) and 200 (F200Y) of the beta tubulin gene in the gastrointestinal nematode, Teladorsagia circumcincta, present in field samples. The molecular identification of this species was confirmed before treatment with albendazole in 6 flocks, amongst other species, but also as the only species surviving treatment. The result of the Faecal Egg Count Reduction Test in these flock ranged between 17-88%, and the resistance was confirmed by the Egg Hatch Assay as well. By pyrosequencing, neither of the two SNPs was present before or after treatment. Therefore, with the aim of confirming these results, a gene fragment of 390bp was sequenced including SNPs at codon 167 (F167Y), 198 and 200 in a pool of L1 recovered before and after treatment in these 6 resistant flocks. Again, in all samples, the three resistance SNPs were absent but a different amino acid was identified at codon 198 in all samples collected after treatment, namely, a leucine (CTA). In the pool of larvae collected before treatment, 5 samples were homozygous G/C and T/A at the first and second base of the codon 198, respectively, leading to the possibility of two amino acids at codon 198, glutamic acid (GAA) or leucine (CTA). In the remaining flock, glutamic acid (GAA) was present before treatment. Further analysis is being performed in individual larvae and other different isolates. All results will be shown at the next COMBAR meeting.