Instituto de Ganadería de Montaña (CSIC-ULE), Finca de Marzanas, 24346 Grulleros, León, Spain.
Vet Parasitol. 2012 Mar 23;184(2-4):371-6. doi: 10.1016/j.vetpar.2011.09.009. Epub 2011 Sep 12.
Benzimidazole (BZ) resistance in gastrointestinal nematodes has been associated with single nucleotide polymorphisms (SNPs) at codons 200, 167 and 198 in the beta-tubulin isotype 1 gene and, recently, these SNPs have also been found in macrocyclic lactone (ML) resistant strains of Haemonchus contortus. On this basis, we have studied the same putative SNPs in Spanish Teladorsagia circumcincta field isolates by pyrosequencing. Single L3 (infective 3rd stage larvae) from five sheep flocks were tested after confirming their BZ susceptibility and degree of ivermectin (IVM) resistance. According to the Faecal Egg Count Reduction Test (FECRT) one flock was classified as IVM susceptible, another one was resistant, and the rest had a suspicion of resistance to IVM. DNA extraction was carried out on 598 single L3 and 56% of these were identified as T. circumcincta after the amplification of a species-specific ITS2 fragment. The number of L3 analyzed for the SNPs 198/200 was 255 and for the SNP 167 was 187. Results clearly indicate no resistance-associated SNPs were present at any codon, before or after treatment. Therefore, all T. cicumcincta L3 were designated as susceptible homozygous genotypes for all SNPs. The absence of the mutations in these populations would argue against resistance haplotypes being present in the parasite population prior to drug treatment, at least in Spanish T. circumcincta.
苯并咪唑（BZ）在胃肠道线虫中的耐药性与β-微管蛋白 1 基因的密码子 200、167 和 198 处的单核苷酸多态性（SNP）有关，最近，这些 SNP 也在大环内酯（ML）耐药的捻转血矛线虫中被发现。在此基础上，我们通过焦磷酸测序研究了西班牙泰莱线虫田间分离株中的相同假定 SNP。在确认其对苯并咪唑的敏感性和伊维菌素（IVM）耐药程度后，从五个绵羊群中测试了单个 L3（感染性 3 期幼虫）。根据粪便卵计数减少试验（FECRT），一个羊群被归类为 IVM 敏感，另一个为耐药，其余的则怀疑对 IVM 耐药。对 598 个单个 L3 进行了 DNA 提取，在扩增了物种特异性 ITS2 片段后，其中 56%被鉴定为泰莱线虫。对 SNP198/200 进行了分析的 L3 数量为 255 个，对 SNP167 进行了分析的 L3 数量为 187 个。结果清楚地表明，在治疗前后，任何密码子都没有与耐药相关的 SNP。因此，所有 T. cicumcincta L3 均被指定为所有 SNP 的敏感纯合基因型。在寄生虫种群中，在药物治疗之前，这些种群中不存在突变，至少在西班牙泰莱线虫中不存在耐药单倍型。
