Page 26 - Science Focus (Issue 017)

Maintaining the gut microbial diversity and balance
Washing hands before meals and is crucial to our health. Low gut bacterial diversity is
cleaning homes with bleach are some of the common correlated with inflammatory bowel disease, diabetes
practices people follow to get rid of germs. While most and obesity [2]. In some cases, antibiotic therapy
people associate microorganisms with diseases and disrupts the original gut microbiome and causes the
infections, they are actually crucial to our health. Our proliferation of the opportunistic pathogen, Clostridium
digestive tract contains trillions of microbes with up difficile, which leads to diarrhea and inflammation
to 1000 species from bacteria, archaea, fungi, of the colon. Fecal microbiota transplantation (FMT)
and protists that aid digestion and help maintain — transplantation of feces (with microbiota) from a
other body functions [1]. Gut microbiota also plays healthy donor to the patient’s colon — has been proved
important roles in other animals. For example, although effective to the patients experiencing devastating and
herbivores have a plant-based diet, not all of them are recurring C. difficile infection [3]. Although it does not
capable of digesting the cellulose in their diet on their sound aesthetically appealing, it helps cure the disease
own. Symbiotic bacteria are often required to break by restoring the ecology of the gut microbiome.
down cellulose to extract glucose for energy.
Besides, the association between specific
While humans, as omnivores, do not rely entirely on microbes and obesity were also discovered.
breaking down cellulose for energy, our gut microbiota The bacteria under the genus Christensenella,
still plays an essential role in our digestion and which was rarely found in overweight people [2],
metabolism. The microbiota is capable of fermenting has been shown to prevent weight gain in mice [4],
indigestible dietary fibers into short-chain fatty while those under Akkermansia correlate with lower
acids (SCFAs), which makes up around 10% of our daily fat deposition near internal organs in human [5].
caloric requirement and serve as the major energy Interestingly, however, the colonization of both species
source for cells lining the colon [1]. Not only do the was suggested to be influenced by host genetics [4, 5].
SCFAs serve as an energy source, but they may serve In other words, not all of us can provide a “good home”
as signals that modulate the ability of human cells to for the beneficial microbes.
handle fat and sugar.

—

Gut Microbiota —

Microorganisms and Our Health

By Kit Kan 簡迎曦

為了消毒殺菌，飯前洗手和用漂白水清潔家居等都是不 維持腸道微生物的多樣性和平衡對我們的健康十分重要。
少人的生活習慣。雖然大部分人都會把微生物與疾病和感染畫 低腸道細菌多樣性與炎症性腸病、糖尿病和肥胖症有關 [2]。在
上等號，但實際上微生物對我們的健康至關重要。我們的消化道 某些情況下，抗生素治療會破壞原本的腸道微生物群系，並導
包含數以萬億計的微生物，其中包括多達 1000 種細菌、古細菌、 致伺機性病原體艱難梭菌（ Clostridium difficile）的增殖，從
真菌和原生生物，它們有助於消化及維持其他身體機能 [1]。腸 而導致腹瀉和結腸發炎。糞便微生物移植（Fecal Microbiota
道菌群在其他動物中也起著重要作用，例如儘管草食動物的食 Transplantation/FMT）是指將糞便（含菌群）從健康捐贈者
物是以植物為基礎，但它們不一定能自行消化植物中的纖維素， 移植到患者的結腸，這方法已被證明對經歷嚴重和復發性艱難
因此通常需要腸道內的共生細菌分解纖維素以提取葡萄糖來獲 梭菌感染的患者有效 [3]。儘管聽起來有點噁心，但糞便微生物
取能量。 移植能夠通過恢復腸道微生物群系的生態來幫助治癒疾病。

雖然人類作為雜食動物並不需依靠分解纖維素來獲取能量， 此外，科學研究亦發現了特定微生物與肥胖之間的關聯。
但我們的腸道菌群仍在我們的消化和代謝中起著至關重要的 克里斯滕森氏菌屬（ Christensenella）的細菌很少在過重的人
作用。微生物群能夠將不能消化的膳食纖維發酵成短鏈脂肪酸 中發現 [2]，研究亦顯示這些細菌可以防止小鼠體重增加 [4]；
(Short Chain Fatty Acids/SCFAs) ，SCFAs 約佔我們每日熱 而阿克曼氏菌屬（ Akkermansia）的細菌則與人體內臟附近的
量需求的 10%，並且是結腸內壁細胞的主要能量來源 [1]。其實 脂肪積聚的減少有關 [5]。但是，有趣的是這兩類細菌的定殖
SCFAs 不僅可以用作能量來源，還可以作為調節人體細胞處理 (colonization) 都受到宿主基因影響 [4, 5]。換句話說，並非所
脂肪和糖的信號。 有人都能為有益的微生物提供合適的「居住環境」。