Sandström G, Sjöstedt A, Forsman M, Pavlovich N V, Mishankin B N
Division of Microbiology, National Defence Research Establishment, Umeå, Sweden.
J Clin Microbiol. 1992 Jan;30(1):172-5. doi: 10.1128/jcm.30.1.172-175.1992.
The two subspecies of Francisella tularensis, F. tularensis subsp. tularensis (type A) and F. tularensis subsp. palaearctica (type B), differ from each other in biochemistry and virulence. Strains of F. tularensis subsp. tularensis are believed to be confined to North America, whereas strains of F. tularensis subsp. palaearctica occur in Europe, in Asia, and in North America. Moreover, the existence of two other subspecies, designated F. tularensis subsp. mediaasiatica and F. tularensis subsp. palaearcitica japonica, has been suggested for strains of F. tularensis isolated in the central Asian focus of the Soviet Union and in Japan, respectively. In the present study, strains biochemically classified as F. tularensis subsp. mediaasiatica or F. tularensis subsp. palaearctica japonica have been investigated by hybridization with probes specific to 16S rRNAs of the two main subspecies. Furthermore, the virulence and biochemical characteristics of the strains were compared with those of strains belonging to F. tularensis subsp. palaearctica and F. tularensis subsp. tularensis. It was found that 16S rRNAs of F. tularensis subsp. mediaasiatica and F. tularensis subsp. palaearctica japonica hybridize with the probe specific to a genotype proposed herein, genotype A (F. tularensis subsp. tularensis), which shows that strains genetically related to this subspecies are found outside North America. However, the central Asian strains differed from F. tularensis subsp. palaearctica and F. tularensis subsp. tularensis strains when investigated by fermentation of glucose. The results of the biochemical tests could not be unambiguously used for differentiation of strains into F. tularensis subsp. palaearctica or F. tularensis subsp. tularensis. These drawbacks suggest that classification of strains of Francisella on the basis of 16S rRNA analysis may be preferable to classification on the basis of biochemical analysis.
土拉弗朗西斯菌的两个亚种，即土拉弗朗西斯菌土拉亚种（A型）和土拉弗朗西斯菌古北区亚种（B型），在生化特性和毒力方面存在差异。土拉弗朗西斯菌土拉亚种的菌株被认为局限于北美洲，而土拉弗朗西斯菌古北区亚种的菌株分布在欧洲、亚洲和北美洲。此外，对于分别在苏联中亚疫源地和日本分离出的土拉弗朗西斯菌菌株，有人提出存在另外两个亚种，分别命名为土拉弗朗西斯菌中亚亚种和土拉弗朗西斯菌日本古北区亚种。在本研究中，通过与针对两个主要亚种的16S rRNA的特异性探针杂交，对生化分类为土拉弗朗西斯菌中亚亚种或土拉弗朗西斯菌日本古北区亚种的菌株进行了研究。此外，还将这些菌株的毒力和生化特性与土拉弗朗西斯菌古北区亚种和土拉弗朗西斯菌土拉亚种的菌株进行了比较。结果发现，土拉弗朗西斯菌中亚亚种和土拉弗朗西斯菌日本古北区亚种的16S rRNA与本文提出的一种基因型（基因型A，即土拉弗朗西斯菌土拉亚种）的特异性探针杂交，这表明在北美洲以外也发现了与该亚种具有遗传相关性的菌株。然而，在通过葡萄糖发酵进行检测时，中亚菌株与土拉弗朗西斯菌古北区亚种和土拉弗朗西斯菌土拉亚种的菌株有所不同。生化试验的结果无法明确用于将菌株区分为土拉弗朗西斯菌古北区亚种或土拉弗朗西斯菌土拉亚种。这些缺陷表明，基于16S rRNA分析对弗朗西斯菌菌株进行分类可能比基于生化分析的分类更可取。
