Benzimidazole -Resistance in Haemonchus contortus: New PCR-RFLP Method for the Detection of Point Mutation at Co¬don 167 of Isotype 1 Β-Tubulin Gene

Due to the lack of a suitable and economic test for the analysis of the polymorphism at codon 167, we developed a new PCR-RFLP technique, based on a modified forward primer (UT-HC167 MF-primer), to identify simultaneously the SNPs at codons 167 and 200 of isotype 1 β-tubu­lin gene of Haemonchus contortus. There already are several safe and easy methods for identification of point mutations at codons 198 and 200. Due to the lack of a reliable and easy method for the detection of the single nucleo­tide polymorphism (SNP) at codon 167, we developed an innovative PCR-RFLP technique based on a modified forward primer (UT-HC167 MF-primer), in which the nucleotide T at the posi­tion 443 was substituted through a nucleotide A creating a restriction site for restriction endonuc­lease SnaB I in the nucleotide sequences including codon 167. A total of 138 adult male H. contortus were collected from three different geo-climatic areas of Iran. The isolated genomic DNA of each single worm was amplified by PCR using primers flanking codon 167. The PCR product (527 bp) was then amplified by semi-nested PCR using the UT-HC167 MF-primer and the reverse primer achiev­ing a PCR product of 451 bp in length. This PCR product was subsequently digested with the restriction endonucleases SnaB I and TaaI for analysis of the mutations at codons 167 and 200, respec­tively. All worms had two alleles encoding for phenylalanine (BZss homozygote) for both codons. Using the UT-HC167 MF-primer and a suitable reverse primer designed upstream from codon 200, it is possible to amplify a PCR product which can be used for analysis of the SNPs at all three mentioned codons using RFLP.