Clark C G, Diamond L S
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Exp Parasitol. 1993 Dec;77(4):456-60. doi: 10.1006/expr.1993.1106.
The reported conversion of "nonpathogenic" Entamoeba histolytica isolates to the "pathogenic" form during attempted axenization of the amebae is highly controversial. After failing to obtain conversions ourselves we concluded that the simplest explanation for the published observations would be contamination of nonpathogenic cultures with pathogenic amebae. To address this possibility we used a method based on analysis of stable DNA polymorphisms that allows the positive identification of individual pathogenic isolates. The DNA patterns obtained using the "converted" amebae proved to be identical to those of reference isolates present in the laboratories at the time of conversion. We also found that very few cells need be transferred for a pathogenic contaminant to become established in a nonpathogenic culture. Cross-contamination fully explains the conversion phenomenon and thus recognition of nonpathogenic and pathogenic amebae as the distinct species Entamoeba dispar Brumpt 1925 and E. histolytica Schaudinn 1903 (Emend. Walker 1911), respectively, is upheld.
在对溶组织内阿米巴进行无菌培养的尝试过程中，有报道称“非致病性”溶组织内阿米巴分离株转变为“致病性”形式，这一说法极具争议。我们自己未能实现这种转变，之后得出结论，对于已发表的观察结果，最简单的解释是致病性阿米巴污染了非致病性培养物。为探究这种可能性，我们采用了一种基于稳定DNA多态性分析的方法，该方法能够对单个致病性分离株进行阳性鉴定。使用“转变后的”阿米巴获得的DNA图谱，经证明与转变时实验室中存在的参考分离株的图谱相同。我们还发现，只需转移极少的细胞，致病性污染物就能在非致病性培养物中定殖。交叉污染充分解释了这种转变现象，因此，分别将非致病性和致病性阿米巴认定为不同的物种——1925年的布氏嗜碘阿米巴（Entamoeba dispar Brumpt）和1903年的溶组织内阿米巴（E. histolytica Schaudinn）（经1911年沃克修订），这一认定得以维持。
