如今,，研究人員發(fā)現(xiàn)幾個世紀(jì)前在歐洲出現(xiàn)的一種細(xì)菌在全球正在擴(kuò)散至經(jīng)歷快速發(fā)展和工業(yè)化的國家。已知隨著發(fā)展中國家變得越來越工業(yè)化,，導(dǎo)致痢疾(dysentery)的弗氏志賀菌(Shigella flexneri)感染數(shù)量在下降,，而且這種下降是與人們健康、生活方式和可能最重要的是獲取清潔的水相關(guān)聯(lián),，但是另一種導(dǎo)致痢疾的細(xì)菌索氏志賀菌(Shigella sonnei)的發(fā)病率實際上卻在增加,。
在這項研究中，研究人員精確地描繪出索氏志賀菌僅在幾個世紀(jì)前在歐洲站穩(wěn)腳跟,，但是在過去幾十年里,，它已擴(kuò)散至世界其他地方。他們在這種病原體擴(kuò)散中發(fā)現(xiàn)一種關(guān)鍵性因素就是多重耐藥性---在接觸一系列抗生素之后仍然存活下來的能力---在上升,。因為索氏志賀菌容易傳播，而且具有高水平的耐藥性,，所以研究人員提示著藥物治療和更好的衛(wèi)生條件并不足以控制疾病的傳播,。疫苗開發(fā)將是非常關(guān)鍵的。
為了研究為什么索氏志賀菌如此有效地傳播,，研究人員研究了它的遺傳進(jìn)化,，發(fā)現(xiàn)只有一些類型的基因選擇性地隨著時間的推移而發(fā)生進(jìn)化，特別是那些參與耐藥性的基因,。這提示著推動這種細(xì)菌擴(kuò)散的主要動力明顯是它能夠?qū)λ幬镏委煯a(chǎn)生耐藥性,。
盡管索氏志賀菌和弗氏志賀菌親緣關(guān)系比較密切，但是它們擁有非常不同的與人免疫系統(tǒng)相互作用的表面抗原或外膜,。索氏志賀菌只有一種類型的外膜,，但是弗氏志賀菌有很多種外膜，而且每種膜看起來與索氏志賀菌明顯不同,。于是科學(xué)家們一直猜測索氏志賀菌在某個時刻從另一種細(xì)菌---志賀鄰單胞菌(Plesiomonas shigelloides)---中獲得它的外膜,，其中志賀鄰單胞菌是一種在污染的水中經(jīng)常被人們發(fā)現(xiàn)的細(xì)菌。
索氏志賀菌和志賀鄰單胞菌擁有完全一樣的外膜,。因此人們認(rèn)為,，一個人當(dāng)接觸到含有志賀鄰單胞菌的污染水時,，就會產(chǎn)生免疫交叉反應(yīng)，因而身體能夠建立起抵抗索氏志賀菌的天然免疫反應(yīng),。這種理論可能解釋著為什么索氏志賀菌的發(fā)病率在經(jīng)濟(jì)發(fā)展和水質(zhì)量改善后會增加,，而且與這項研究中描述的全球擴(kuò)散模式相一致。(生物谷：Bioon.com)
本文編譯自Researchers look at the spread of dysentery from Europe to industrializing countries
doi: 10.1038/ng.2369
PMC:
PMID:
Shigella sonnei genome sequencing and phylogenetic analysis indicate recent global dissemination from Europe
Kathryn E Holt, Stephen Baker, François-Xavier Weill, Edward C Holmes, Andrew Kitchen, Jun Yu, Vartul Sangal, Derek J Brown, John E Coia, Dong Wook Kim, Seon Young Choi, Su Hee Kim, Wanderley D da Silveira, Derek J Pickard, Jeremy J Farrar, Julian Parkhill, Gordon Dougan & Nicholas R Thomson
Shigella are human-adapted Escherichia coli that have gained the ability to invade the human gut mucosa and cause dysentery1, 2, spreading efficiently via low-dose fecal-oral transmission3, 4. Historically, S. sonnei has been predominantly responsible for dysentery in developed countries but is now emerging as a problem in the developing world, seeming to replace the more diverse Shigella flexneri in areas undergoing economic development and improvements in water quality4, 5, 6. Classical approaches have shown that S. sonnei is genetically conserved and clonal7. We report here whole-genome sequencing of 132 globally distributed isolates. Our phylogenetic analysis shows that the current S. sonnei population descends from a common ancestor that existed less than 500 years ago and that diversified into several distinct lineages with unique characteristics. Our analysis suggests that the majority of this diversification occurred in Europe and was followed by more recent establishment of local pathogen populations on other continents, predominantly due to the pandemic spread of a single, rapidly evolving, multidrug-resistant lineage.
