Gastrointestinal Colonization of Fungi
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TRANSLATIONAL RESEARCH (R WHEELER, SECTION EDITOR)
Gastrointestinal Colonization of Fungi Andrew Y. Koh
Published online: 14 March 2013 # Springer Science+Business Media New York 2013
Abstract The human gastrointestinal tract is colonized with trillions of commensal microbes, and disturbances in the equilibrium of the gut microbiota have now been shown to be associated with a number of human diseases. Fungi, particularly Candida spp., are normal, harmless residents of the human gut, but in certain instances can cause invasive infections and inflammatory disorders. This paper will review the fungal diversity in the human gut, host and fungal factors that regulate GI colonization, and how these factors play into the pathogenesis of human disease. Keywords Gastrointestinal . Colonization . Pathobiont . Commensal . Microbiota . Candida . Inflammatory bowel disease . Th17 . Dectin
Introduction The human body is colonized by microbial organisms on essentially all environmentally exposed surfaces, with the vast majority colonizing the gastrointestinal (GI) tract. Commensal microbes can outnumber host cells by a factor of 10 to 1 and aid in many essential host functions, such as synthesis of vitamins, nutrient processing, maintenance of the intestinal epithelial barrier, and resistance to pathogen colonization [1]. Not all host–microbiota interactions, however, promote health. In fact, there are some symbiotic microorganisms in the GI tract that can induce human pathology under specific conditions, typically involving environmental and/or genetic changes; and the term “pathobionts” has been coined to describe resident microbes with pathogenic potential [2]. In contrast to traditional pathogens which may cause disease in a normal healthy host, pathobionts are harmless to the host under normal conditions. A. Y. Koh (*) Department of Pediatrics and Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9063, USA e-mail: [email protected]
Although the human GI tract is dominated by bacteria, microbes from other domains, notably Archaea and Eukarya, are present in the human intestine [3]. While high-throughput sequencing technology has provided great insight into the characterization of the vast bacterial communities in the human GI tract, the eukaryotic component of the human gut remains relatively unexplored. Initial cultureindependent low-throughput methods (i.e., community finger printing and clone library sequencing) have revealed some important insights: (1) fungi and Blastocystis (single celled protozoan parasites) appear to be the dominant, and in many cases the only, eukaryotes in the gut of healthy individuals [4–6]; (2) the diversity of microbial eukaryotes within an individual is low, with fewer than 10 phylotypes recovered per individual [5, 6]; and (3) the limited data suggests that eukaryotic communities are stable across time and unique to individuals [6]. The remainder of this review will focus on examining the normal fungal populations inhabit
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