Tang Swee-Seong, Carlin Nils I A, Talukder Kaisar A, Cam Phung D, Verma Naresh K
Division of Biomedical Science and Biochemistry, Research School of Biology, The Australian National University, Bldg #134 Linnaeus Way, Canberra, ACT 0200, Australia.
Division of Microbiology, Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia.
BMC Microbiol. 2016 Jun 27;16(1):127. doi: 10.1186/s12866-016-0746-z.
Shigella spp. are the primary causative agents of bacillary dysentery. Since its emergence in the late 1980s, the S. flexneri serotype 1c remains poorly understood, particularly with regard to its origin and genetic evolution. This article provides a molecular insight into this novel serotype and the gtrIC gene cluster that determines its unique immune recognition.
A PCR of the gtrIC cluster showed that serotype 1c isolates from different geographical origins were genetically conserved. An analysis of sequences flanking the gtrIC cluster revealed remnants of a prophage genome, in particular integrase and tRNA(Pro) genes. Meanwhile, Southern blot analyses on serotype 1c, 1a and 1b strains indicated that all the tested serotype 1c strains may have had a common origin that has since remained distinct from the closely related 1a and 1b serotypes. The identification of prophage genes upstream of the gtrIC cluster is consistent with the notion of bacteriophage-mediated integration of the gtrIC cluster into a pre-existing serotype.
This is the first study to show that serotype 1c isolates from different geographical origins share an identical pattern of genetic arrangement, suggesting that serotype 1c strains may have originated from a single parental strain. Analysis of the sequence around the gtrIC cluster revealed a new site for the integration of the serotype converting phages of S. flexneri. Understanding the origin of new pathogenic serotypes and the molecular basis of serotype conversion in S. flexneri would provide information for developing cross-reactive Shigella vaccines.
志贺氏菌属是细菌性痢疾的主要病原体。自20世纪80年代末出现以来，福氏志贺氏菌1c血清型仍未得到充分了解，尤其是其起源和基因进化方面。本文对这种新型血清型以及决定其独特免疫识别的gtrIC基因簇进行了分子层面的深入研究。
gtrIC基因簇的聚合酶链反应（PCR）显示，来自不同地理区域的1c血清型分离株在基因上具有保守性。对gtrIC基因簇侧翼序列的分析揭示了一个前噬菌体基因组的残余部分，特别是整合酶和tRNA(Pro)基因。同时，对1c、1a和1b血清型菌株的Southern印迹分析表明，所有测试的1c血清型菌株可能有一个共同的起源，并且与密切相关的1a和1b血清型保持不同。gtrIC基因簇上游前噬菌体基因的鉴定与噬菌体介导的gtrIC基因簇整合到预先存在的血清型这一概念相一致。
这是第一项表明来自不同地理区域的1c血清型分离株具有相同基因排列模式的研究，表明1c血清型菌株可能起源于单一亲本菌株。对gtrIC基因簇周围序列的分析揭示了福氏志贺氏菌血清型转换噬菌体整合的新位点。了解新致病血清型的起源以及福氏志贺氏菌血清型转换的分子基础将为开发交叉反应性志贺氏菌疫苗提供信息。
