Department of Microbiology, University of Dhaka, Dhaka, Bangladesh.
Curr Microbiol. 2011 Oct;63(4):372-6. doi: 10.1007/s00284-011-9992-3. Epub 2011 Aug 9.
Little is known about the distribution, survival, and transmission of Shigella in environmental surface waters. To gain more insight into the environmental biology of Shigella we isolated five bacterial strains serotyped as Shigella flexneri 2b from a freshwater lake in Bangladesh using a modified nutrient broth supplemented with nucleic acid bases. The biochemical properties of the isolates, including inability to ferment lactose and a negative lysine decarboxylase test, indicated common physiological characteristics with Shigella, but differed significantly from that of standard clinical strains. The isolates possessed the ipaH virulence gene and a megaplasmid, but lacked other Shigella-related virulence marker genes. Genetic fingerprinting and sequence analysis of housekeeping genes confirmed the strains as S. flexneri isolates. An apparent clonal origin of strains recovered with a one-year interval indicates a strong environmental selection pressure on Shigella for persistence in the freshwater environment. The lack of a complete set of virulence genes as well as uncommon biochemical properties suggest that these strains might represent a group of non-invasive and atypical environmental Shigella variants, with the potential for further elucidation of the survival mechanism, diversity, and emergence of virulent Shigella in tropical freshwater environments.
关于志贺氏菌在环境地表水的分布、存活和传播情况知之甚少。为了更深入地了解志贺氏菌的环境生物学特性，我们使用改良的营养肉汤从孟加拉国的一个淡水湖中分离出 5 株血清型为福氏 2b 志贺氏菌的细菌，该肉汤补充了核酸碱基。分离株的生化特性，包括不能发酵乳糖和赖氨酸脱羧酶试验阴性，表明与志贺氏菌具有共同的生理特征，但与标准临床株有显著差异。这些分离株携带 ipaH 毒力基因和一个巨大质粒，但缺乏其他与志贺氏菌相关的毒力标记基因。看家基因的遗传指纹图谱和序列分析证实了这些菌株是福氏志贺氏菌的分离株。相隔一年回收的菌株具有明显的克隆起源，表明志贺氏菌在淡水环境中持续存在受到强烈的环境选择压力。缺乏一套完整的毒力基因以及不常见的生化特性表明，这些菌株可能代表一组非侵袭性和非典型的环境志贺氏菌变体，有可能进一步阐明在热带淡水环境中生存机制、多样性和毒力志贺氏菌的出现。
