The Human Microbiome: From Symbiosis to Pathogenesis
Human Commensal and Mutual Organisms From the moment of birth and throughout our It is often difficult to identify a relationship between organisms as purely it is often difficult to distinguish between true commensalism and mutualism. Transition from commensalism to parasitism is dependent on host, environmental and fungal .. The symbiotic relationship between humans and fungi is greatly. There are three types of symbiotic relationships in which humans and bacteria coexist. The types of symbiosis are termed commensalism.
The fungal genus Aspergillus is capable of living under considerable environmental stress, and thus is capable of colonising the upper gastrointestinal tract where relatively few examples of the body's gut flora can survive due to highly acidic or alkaline conditions produced by gastric acid and digestive juices. While Aspergillus normally produces no symptoms, in individuals who are immunocompromised or suffering from existing conditions such as tuberculosisa condition called aspergillosis can occur, in which populations of Aspergillus grow out of control.
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Staphylococcus aureusa common bacterial species, is known best for its numerous pathogenic strains that can cause numerous illnesses and conditions. However, many strains of S.
Other Staphylococcus species including S. Arguments[ edit ] Whether the relationship between humans and some types of gut flora is commensal or mutualistic is still unanswered.Interactions between populations - Ecology - Khan Academy
Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party, and that relationships identified as commensal are likely mutualistic or parasitic in a subtle way that has not been detected.
For example, epiphytes are "nutritional pirates" that may intercept substantial amounts of nutrients that would otherwise go to the host plant. Similarly, phoretic mites may hinder their host by making flight more difficult, which may affect its aerial hunting ability or cause it to expend extra energy while carrying these passengers.
The role of human-associated microbiota in health and disease has received newfound appreciation owing to our ability to quantify and qualify the types and the metabolic and functional capabilities of the microbial consortia associated with our bodies 6. For example, a critical link has recently been established for the resident gastrointestinal microbiota in the promotion of atherosclerosis 7.
Wang and colleagues 7 delineated a two-step metabolic pathway involving the microbially mediated metabolism of dietary phosphatidylcholine, resulting in the production of the metabolite trimethylamine N-oxide TMAOa predictor of cardiovascular disease CVD risk.
Additionally, a recent study by Sellitto et al. This study also highlighted the utility of incorporating studies of the metabolic capabilities of the microbiota, resulting in the potential identification of biomarkers for the development of celiac disease 8. Development of a mechanistic understanding of the human microbiota in relation to human health and disease and incorporation of the microbiome as a key component of the entire human genomic framework are fundamental for the advancement of personalized medicine.
Concomitant with technological advances, the application of ecological theory to the host— microbiota system has generated profound insight into human health. The human microbiota performs essential functions that define and contribute to the physiology of the host, sharing a unique biological relationship termed a symbiosis.
In the human microbiome literature, the definition of symbiosis ranges from a commensalistic relationship, wherein the interaction is decidedly beneficial for one of the partners the hostto mutualistic, involving beneficial outcomes for all organisms involved.
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In this review, we discuss the variety of symbiotic interactions of the human host and microbiota in the context of maintaining homeostasis, focusing on the host—microbiota systems of the vagina and gastrointestinal tract, and how perturbations of these interactions lead to dysbiosis.
Tools and Technologies to Access our Microbiota In many complex communities, the majority of the microbial members identified using molecular techniques have resisted cultivation efforts Human eyes are covered with a specialized skin that is bathed in tears, and only a few microbes can survive these conditions.
- Human Commensal and Mutual Organisms
- Skin and Eyes
Corynebacteria such as Corynebacterium xerosis can establish themselves as resident commensals on human cornea. Digestive Tract The mouth provides a number of ecological niches where microscopic organisms can colonize. Dental caries tooth decay are caused by the interaction between commensal bacteria and sugar in the diet. Streptococcus mutans converts sugar into slime which sticks firmly to the enamel of the teeth, beginning the decay process.
The crevices between the gum and teeth also harbor bacteria such as Bacteroides and Fusobacterium that can cause gum disease. Commensal organisms usually do not colonize the stomach because it is highly acidic, although some acid-tolerant lactobacilli can live there.
One bacteria, Helicobacter pylori, has recently been linked with ulcer formation in some people. The normal flora of the intestines, Eschericia coli, Streptococcus, and Bacteroides contribute to the normal functioning of the digestive system. The importance of the role of these organisms becomes more evident when the administration of antibiotics or laxatives kills them.
Without these organisms, the digestive system may be colonized by pathogenic bacteria that are resistant to antibiotics.
Respiratory Tract The respiratory tract is anatomically complex and constantly exposed to microorganisms in the air breathed in. The microflora of our nostrils resembles that of the skin, with colonies of commensal organisms such as micrococci, corynebacteria, staphlococci, and streptococci.
Streptococcus pyogenes is part of the commensal flora of the nose in healthy individuals, but may cause tonsillitis and strep throat. The warm, moist environment of the upper respiratory tract provides a haven for commensal bacteria including Streptococcus, Moraxella, Neisseria, and Haemophplus, species.
The lower respiratory tract is generally free from microorganisms, mainly because of the efficient action of the cilia that line the tract. Roles of Commensal and Mutual Organisms Nineteenth-century French microbiologist Louis Pasteur believed that animals cannot exist without a population of commensal and mutual organisms, and early experiments to raise germ-free animals met with failure.
All germ-free animals have weak, poorly developed immune systems. This suggests that the roles of normal microscopic organisms are very important.
Commensal organisms play a significant role in preventing infections. This may be simply because they deny the invading organism access to the target site, or because the benign organism actively produces substances that inhibit the growth of, or even kill, other organisms.
Commensal flora and fauna may also "switch roles" and become an important source of infection for the human host.