從細菌多樣性程度來說,，腸道堪稱人體內(nèi)的熱帶雨林,。日前，發(fā)表在美國《公共科學圖書館·生物學》雜志(PLoS biology)上的一篇文章稱,，人類腸道內(nèi)的細菌群落數(shù)量是原有認識的10倍以上,。
單從數(shù)量上來說，哺乳動物結腸內(nèi)的細菌群落密度堪稱地球之最,。人體內(nèi)共有細胞約100萬億個(成年人),，細菌數(shù)量則是細胞的10倍，超過1000萬億個,，而這些細菌大多集中在人類消化道中,。
以前，科學家估算人體細菌種類的方法是從腸道中提取細菌,，然后在培養(yǎng)皿上培養(yǎng),，待菌落長出后，再進行計數(shù),。利用這種方法得到的數(shù)據(jù)是,，人體內(nèi)大約有500種細菌。但這種方法有個無法彌補的缺陷：只能計算可以在培養(yǎng)皿中生長的常見菌落的數(shù)量,，對于無法在體外環(huán)境中生長的罕見細菌,，則無法計數(shù)。因此,，“人體內(nèi)有500種細菌”的結論并不準確,。
美國斯坦福大學醫(yī)學院的戴維·雷爾曼(David Relman)和同事一起，利用一種新型技術——焦磷酸測序法(pyrosequencing),，得到了關于人體腸道內(nèi)菌落數(shù)量更為準確的數(shù)據(jù),。雷爾曼說：“焦磷酸測序法以前是用于評估海底環(huán)境中細菌生態(tài)系統(tǒng)的豐度，我們首次將這種技術用于評估人體內(nèi)部的‘生態(tài)系統(tǒng)’,。”
利用焦磷酸測序法為細菌分類時,，研究人員首先要提取大量待檢測細菌的DNA片段(這些片段一般編碼某些常見分子)，在根據(jù)片段上的變異情況,，對細菌進行分類,。
論文第一作者、雷爾曼實驗室的博士后研究人員雷斯·德特雷福森(Les Dethlefsen)說：“比起培養(yǎng)鑒別法,，這種新的基因測序技術能檢測到更多的細菌種類,。”
雷爾曼等人發(fā)現(xiàn)，人體腸道內(nèi)的細菌種類遠超人們想象,，至少有5600個細菌群落,。他們的這項研究得到了美國自然科學基金會和美國國立衛(wèi)生研究院的資助。
對于人體健康，腸道細菌發(fā)揮著重要作用：分解食物,、微調(diào)免疫系統(tǒng),、分泌維生素K等營養(yǎng)物質(zhì)、“吞”掉食物殘渣……另外,，細菌數(shù)量多還可以讓致病菌沒有立足之地,。
近些年，醫(yī)生為病人開的抗生素越來越多,。很多科學家擔心,，人們經(jīng)常服用抗生素類藥物，會使腸道細菌數(shù)量減少,，甚至可能產(chǎn)生更多的具有耐藥性的致病菌,。雷爾曼和德特雷福森希望，焦磷酸測序法進一步用于評估抗生素對腸道有益菌和人體健康的影響,。（生物谷Bioon.com）
生物谷推薦原始出處：
PLoS biology,，doi:10.1371/journal.pbio.0060280，Les Dethlefsen,，David A. Relman
The Pervasive Effects of an Antibiotic on the Human Gut Microbiota, as Revealed by Deep 16S rRNA Sequencing
Les Dethlefsen1,2, Sue Huse3, Mitchell L. Sogin3, David A. Relman1,2,4*
1 Department of Microbiology and Immunology, Stanford University, Stanford, California, United States of America, 2 Department of Medicine, Stanford University, Stanford, California, United States of America, 3 Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, Massachusetts, United States of America, 4 Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
The human intestinal microbiota is essential to the health of the host and plays a role in nutrition, development, metabolism, pathogen resistance, and regulation of immune responses. Antibiotics may disrupt these coevolved interactions, leading to acute or chronic disease in some individuals. Our understanding of antibiotic-associated disturbance of the microbiota has been limited by the poor sensitivity, inadequate resolution, and significant cost of current research methods. The use of pyrosequencing technology to generate large numbers of 16S rDNA sequence tags circumvents these limitations and has been shown to reveal previously unexplored aspects of the “rare biosphere.” We investigated the distal gut bacterial communities of three healthy humans before and after treatment with ciprofloxacin, obtaining more than 7,000 full-length rRNA sequences and over 900,000 pyrosequencing reads from two hypervariable regions of the rRNA gene. A companion paper in PLoS Genetics (see Huse et al., doi: 10.1371/journal.pgen.1000255) shows that the taxonomic information obtained with these methods is concordant. Pyrosequencing of the V6 and V3 variable regions identified 3,300–5,700 taxa that collectively accounted for over 99% of the variable region sequence tags that could be obtained from these samples. Ciprofloxacin treatment influenced the abundance of about a third of the bacterial taxa in the gut, decreasing the taxonomic richness, diversity, and evenness of the community. However, the magnitude of this effect varied among individuals, and some taxa showed interindividual variation in the response to ciprofloxacin. While differences of community composition between individuals were the largest source of variability between samples, we found that two unrelated individuals shared a surprising degree of community similarity. In all three individuals, the taxonomic composition of the community closely resembled its pretreatment state by 4 weeks after the end of treatment, but several taxa failed to recover within 6 months. These pervasive effects of ciprofloxacin on community composition contrast with the reports by participants of normal intestinal function and with prior assumptions of only modest effects of ciprofloxacin on the intestinal microbiota. These observations support the hypothesis of functional redundancy in the human gut microbiota. The rapid return to the pretreatment community composition is indicative of factors promoting community resilience, the nature of which deserves future investigation.
