The Human Microbiome: A New Frontier in Health (Mayo 2024)
Human microbiome, ang buong hanay ng mga microorganism (ang microbiota) na naninirahan at sa mga tao at, lalo na, ang koleksyon ng mga mikrobyong genom na nag-aambag sa mas malawak na larawan ng genetic, o metagenome, ng isang tao. Ang mga genom na bumubuo sa microbiome ng tao ay kumakatawan sa isang napaka-magkakaibang hanay ng mga microorganism na may kasamang bakterya, archaea (primitive na single-celled na organismo), fungi, at kahit na ilang mga protozoan at hindi nagbibigay ng mga virus. Ang bakterya ay higit sa maraming mga miyembro ng microbiome ng tao: ang populasyon ng bakterya lamang ay tinatayang sa pagitan ng 75 trilyon at 200 trilyon na mga indibidwal na organismo, habang ang buong katawan ng tao ay binubuo ng halos 50 trilyon hanggang 100 trilyon na somatic (body) cells. Ang manipis na kasaganaan ng microbial ay nagmumungkahi na ang katawan ng tao ay sa katunayan isang "supraorganism,"Isang koleksyon ng mga selula ng tao at microbial at gen at sa gayon isang timpla ng mga katangian ng tao at microbial.
Natuklasan ng microbiome ng tao
Ang unang pang-agham na katibayan na ang mga microorganism ay bahagi ng normal na sistema ng tao na lumitaw noong kalagitnaan ng 1880s, nang naobserbahan ng pedyatrisyan na si Theodor Escherich ang Austrian pediatrician na si Theodor Escherich) sa isang bituka na flora ng malusog na mga bata at mga bata na apektado ng sakit na diarrheal. Sa mga sumunod na taon, inilarawan ng mga siyentipiko ang maraming iba pang mga microorganism na nakahiwalay mula sa katawan ng tao, kasama na noong 1898 ang species na Veillonella parvula, isang bacterial member ng oral, digestive, urinary, at upper respiratory flora, at noong 1900 bifidobacteria, mga miyembro ng ang bituka flora. Sa buong ika-20 siglo isang bilang ng iba pang mga microorganism ay nakahiwalay mula sa mga sipi ng ilong, oral cavities, balat, gastrointestinal tract, at urogenital tract at nailalarawan bilang bahagi ng microbiota ng tao.Bagaman ang pangkat na ito ng mga organismo ay na-conceptualize sa iba't ibang mga paraan mula nang natuklasan, ang konsepto ng microbiome ng tao, at sa gayon ang masinsinang pag-aaral nito, ay una na binuo sa unang dekada ng ika-21 siglo.
Knowledge of the human microbiome expanded appreciably after 2007, the year the Human Microbiome Project (HMP)—a five-year-long international effort to characterize the microbial communities found in the human body and to identify each microorganism’s role in health and disease—was launched. The project capitalized on the decreasing cost of whole genome sequencing technology, which allows organisms to be identified from samples without the need for culturing them in the laboratory; the technology also facilitates the process of comparing DNA sequences of microorganisms isolated from different parts of the human body and from different people. In the first three years of the project, scientists discovered new members of the human microbiota and characterized nearly 200 different bacterial member species.
Microbial diversity
By some estimates, the human microbiota may consist of a total of 900 or 1,000 different species of microorganisms, making for an extraordinarily diverse collection of microbial genomes. This diversity manifests in differences in microbial composition not only from one human to the next but also between matching body parts, such as the right and left hands, of the same individual. For example, as one study has shown, a typical palm surface of the hand can harbour more than 150 different bacterial species, only 17 percent of which are common to both hands of the same person and only 13 percent of which are shared by different persons.
The human gut is another site characterized by a high degree of microbiome diversity and abundance. In a study of 124 European individuals, researchers isolated some 3.3 million microbial genes. Many of these genes represented frequently occurring bacterial gut species, at least 160 of which were believed to inhabit each person’s gut. The identification of such frequently occurring species in populations is fundamental to defining so-called common bacterial cores, which enable scientists to explore the interface of the human microbiome with factors such as diet, culture, and genotype (genetic makeup).
The role of the human microbiota
Most members of the human microbiota benefit humans by providing them with traits that they would not otherwise possess. Some microorganisms found in the human gut, for instance, obtain nutrients from ingested food in return for assisting with the breakdown of food or preventing the colonization of the gut by harmful bacteria. There are, however, many microorganisms in the human microbiota that are closely related to pathogenic (disease-causing) organisms or are themselves capable of becoming pathogenic. Examples include bacterial species of the genera Staphylococcus, Streptococcus, Enterococcus, Klebsiella, Enterobacter, and Neisseria.
Clostridium difficile infectionserves as a useful example for illustrating the significance of the relationship between the human microbiome and health and disease. C. difficile infection, which is characterized by severe recurrent diarrhea, abdominal cramping, and nausea, occurs most often in persons who receive a course of antibiotics while in a hospital. Antibiotics kill or inhibit the reproduction of pathogenic bacteria and in the process cause dramatic changes in normal human microbial communities, such that previously established colonies may be overtaken by colonies of different and potentially pathogenic species. In the case of C. difficile, researchers have discovered that infection can be treated effectively through fecal, or stool, transplantation, in which fecal material from a healthy person is transferred to the patient, thereby restoring populations of beneficial gut microbiota.
Scientists studying obesity have detected an increased abundance of Prevotella and Firmicutes bacteria and of methanogenic (methane-producing) archaea in obese individuals relative to normal-weight persons and persons who have undergone gastric bypass surgery. Scientists suspect that these microorganisms are more efficient at harvesting carbohydrates from food than are the types of microorganisms that dominate the gut flora of normal-weight individuals. The extra nutrients are then stored in the body as fat.
Ongoing study of the human microbiome is expected to continue to shed light on fundamental aspects of human physiology and particularly human nutrition. Improved understanding of nutritional requirements could lead to changes in dietary recommendations and in food production. In addition, information about the human microbiome could lead to the development of new diagnostic techniques and treatments for a variety of human diseases, as well as to the development of industrial products based on substances (e.g., enzymes) that are produced by members of the human microbiota.
