Fazaeli A, Ebrahimzadeh A
Department of Medical Parasitology and Mycology, Medical School, Zahedan University of Medical Sciences, Mashahir Square, Zahedan 98165, Iran.
Parasitol Res. 2007 Jun;101(1):99-104. doi: 10.1007/s00436-006-0449-8. Epub 2007 Feb 13.
SAG2 locus, the coding gene of the P22 protein, has been widely used for the molecular epidemiology of Toxoplasma gondii and characterization of the parasite isolates with two separate polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) processes. To re-assess the resolution power and suitability of this genetic marker for molecular characterization of the parasite isolates, a number of 27 Toxoplasma strains from different zymodeme patterns were used in the present study. Both codon and non-codon regions of the SAG2 locus of all 27 strains were amplified and subjected to sequencing and nucleotide alignment. Nucleotide variations clustered the three major genotypes (I, II and III). Some minor genotypes, unidentifiable by SAG2-RFLP, could be identified by sequence comparison. However, there were other genotypes that could not be differentiated from the major types due to having identical sequences. This suggests that a remarkable number of field isolates representing several minor types will be miss-clustered with the major types by using the traditional SAG2-PCR-RFLP method. It was concluded that this technique seems not to be suitable for Toxoplasma population study. Thus, the utilization of more variable markers and other discriminatory methods are also recommended.
SAG2位点是P22蛋白的编码基因，已被广泛用于弓形虫的分子流行病学研究以及通过两种独立的聚合酶链反应（PCR）-限制性片段长度多态性（RFLP）方法对寄生虫分离株进行特征分析。为了重新评估该遗传标记对寄生虫分离株分子特征分析的分辨能力和适用性，本研究使用了来自不同酶谱模式的27株弓形虫菌株。对所有27株菌株的SAG2位点的密码子和非密码子区域进行扩增，并进行测序和核苷酸比对。核苷酸变异将三种主要基因型（I、II和III）聚类。一些通过SAG2-RFLP无法识别的次要基因型，可以通过序列比较来识别。然而，由于序列相同，还有其他基因型无法与主要类型区分开来。这表明，使用传统的SAG2-PCR-RFLP方法，相当数量代表几种次要类型的野外分离株将与主要类型错误聚类。得出的结论是，该技术似乎不适用于弓形虫种群研究。因此，也建议使用更多可变标记和其他鉴别方法。
