Sundin Olof H, Mendoza-Ladd Antonio, Zeng Mingtao, Diaz-Arévalo Diana, Morales Elisa, Fagan B Matthew, Ordoñez Javier, Velez Philip, Antony Nishaal, McCallum Richard W
Department of Biomedical Sciences, Texas Tech University Health Sciences Center at El Paso, El Paso, 79905, TX, USA.
Department of Internal Medicine, Division of Gastroenterology, Texas Tech University Health Sciences Center at El Paso, El Paso, 79905, TX, USA.
BMC Microbiol. 2017 Jul 17;17(1):160. doi: 10.1186/s12866-017-1059-6.
The upper half of the human small intestine, known as the jejunum, is the primary site for absorption of nutrient-derived carbohydrates, amino acids, small peptides, and vitamins. In contrast to the colon, which contains 10-10 colony forming units of bacteria per ml (CFU/ml), the normal jejunum generally ranges from 10 to 10 CFU per ml. Because invasive procedures are required to access the jejunum, much less is known about its bacterial microbiota. Bacteria inhabiting the jejunal lumen have been investigated by classical culture techniques, but not by culture-independent metagenomics.
The lumen of the upper jejunum was sampled during enteroscopy of 20 research subjects. Culture on aerobic and anaerobic media gave live bacterial counts ranging from 5.8 × 10 CFU/ml to 8.0 × 10 CFU/ml. DNA from the same samples was analyzed by 16S rRNA gene-specific quantitative PCR, yielding values from 1.5 × 10 to 3.1 × 10 bacterial genomes per ml. When calculated for each sample, estimated bacterial viability ranged from effectively 100% to a low of 0.3%. 16S rRNA metagenomic analysis of uncultured bacteria by Illumina MiSeq sequencing gave detailed microbial composition by phylum, genus and species. The genera Streptococcus, Prevotella, Veillonella and Fusobacterium, were especially abundant, as well as non-oral genera including Escherichia, Klebsiella, and Citrobacter. The jejunum was devoid of the genera Alistipes, Ruminococcus, Faecalibacterium, and other extreme anaerobes abundant in the colon. In patients with higher bacterial loads, there was no significant change in microbial species composition.
The jejunal lumen contains a distinctive bacterial population consisting primarily of facultative anaerobes and oxygen-tolerant obligate anaerobes similar to those found in the oral cavity. However, the frequent abundance of Enterobacteriaceae represents a major difference from oral microbiota. Although a few genera are shared with the colon, we found no evidence for retrograde movement of the most abundant colonic microbes to the jejunum. Some individuals had much higher bacterial loads, but this was not correlated with decreases in bacterial species diversity or other evidence of dysbiosis.
人类小肠的上半部分即空肠，是营养衍生的碳水化合物、氨基酸、小肽和维生素吸收的主要部位。与每毫升含有10⁸ - 10¹⁰菌落形成单位（CFU/ml）细菌的结肠相比，正常空肠中的细菌数量通常为每毫升10²至10⁷CFU。由于需要侵入性操作才能进入空肠，因此对其细菌微生物群的了解要少得多。以往曾采用经典培养技术研究空肠腔中的细菌，但未采用不依赖培养的宏基因组学方法。
在对20名研究对象进行小肠镜检查期间，采集了空肠上段的肠腔样本。在需氧和厌氧培养基上培养得到的活菌计数范围为5.8×10²CFU/ml至8.0×10⁷CFU/ml。对相同样本的DNA进行16S rRNA基因特异性定量PCR分析，得到每毫升1.5×10⁵至3.1×10⁷个细菌基因组的值。对每个样本进行计算时，估计的细菌存活率范围从实际上的100%到低至0.3%。通过Illumina MiSeq测序对未培养细菌进行16S rRNA宏基因组分析，按门、属和种给出了详细的微生物组成。链球菌属、普雷沃菌属、韦荣球菌属和梭杆菌属特别丰富，还有包括大肠杆菌属、克雷伯菌属和柠檬酸杆菌属在内的非口腔菌属。空肠中不存在结肠中丰富的阿利斯杆菌属、瘤胃球菌属、粪杆菌属和其他极端厌氧菌。在细菌载量较高的患者中，微生物种类组成没有显著变化。
空肠腔含有独特的细菌群体，主要由兼性厌氧菌和耐氧专性厌氧菌组成，类似于口腔中发现的细菌。然而，肠杆菌科细菌的频繁大量存在是与口腔微生物群的主要差异。虽然有一些菌属与结肠共有，但我们没有发现最丰富的结肠微生物逆行至空肠的证据。一些个体的细菌载量要高得多，但这与细菌物种多样性的降低或其他生态失调证据无关。
