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''Candida albicans'' is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans, and candidal onychomycosis, an infection of the nail plate. Systemic fungal infections (fungemias) including those by ''C. albicans'' have emerged as important causes of morbidity and mortality in immunocompromised patients (e.g., AIDS, cancer chemotherapy, organ or bone marrow transplantation). ''C. albicans'' biofilms may form on the surface of implantable medical devices. In addition, hospital-acquired infections by ''C. albicans'' have become a cause of major health concerns. About 85-95 % of vaginal infections cases are responsible for physician office visits every year. ''C. albicans'' is commensal and a constituent of the normal gut flora comprising microorganisms that live in the human mouth and gastrointestinal tract. Overgrowth of the fungus results in candidiasis (candidosis). Candidiasis is often observed in immunocompromised individuals, including HIV-infected patients. A common form of candidiasis restricted to the mucosal membranes in mouth or vagina is thrush, which is usually easily cured in people who are not immunocompromised. For example, higher prevalence of colonization of ''C. albicans'' was reported in young individuals with tongue piercing, in comparison to unpierced matched individuals. To infect host tissue, the usual unicellular yeast-like form of ''C. albicans'' reacts to environmental cues and switches into an invasive, multicellular filamentous form, a phenomenon called dimorphism.〔 In addition, an overgrowth infection is considered superinfection,usually applied when an infection become opportunistic and very resistant to antifungals. It then becomes suppressed by antibiotics. The infection is prolonged when the original sensitive strain is replaced by the antibiotic-resistant strain. ==Genome== One of the most important features of the ''C. albicans'' genome is the occurrence of numeric and structural chromosomal rearrangements as means of generating genetic diversity, named chromosome length polymorphisms (contraction/expansion of repeats), reciprocal translocations, chromosome deletions and trisomy of individual chromosomes. These karyotypic alterations lead to changes in the phenotype, which is an adaptation strategy of this fungus. These mechanisms will be better understood with the complete analysis of the ''C. albicans'' genome. An unusual feature of the ''Candida'' genus is that in many of its species (including ''C. albicans'' and ''C. tropicalis'', but not, for instance, ''C. glabrata'') the CUG codon, which normally specifies leucine, specifies serine in these species. This is an unusual example of a departure from the standard genetic code, and most such departures are in start codons or, for eukaryotes, mitochondrial genetic codes. This alteration may, in some environments, help these ''Candida'' species by inducing a permanent stress response, a more generalized form of the heat shock response. The genome of ''C. albicans'' is highly dynamic, and this variability has been used advantageously for molecular epidemiological studies and population studies in this species. The genome sequence has allowed for identifying the presence of a parasexual cycle (no detected meiotic division) in ''C. albicans''. This study of the evolution of sexual reproduction in six ''Candida'' species found recent losses in components of the major meiotic crossover-formation pathway, but retention of a minor pathway.〔 The authors suggested that if ''Candida'' species undergo meiosis it is with reduced machinery, or different machinery, and indicated that unrecognized meiotic cycles may exist in many species. In another evolutionary study, introduction of partial CUG identity redefinition (from ''Candida'' species) into ''Saccharomyces cerevisiae'' clones caused a stress response that negatively affected sexual reproduction. This CUG identity redefintion, occurring in ancestors of ''Candida'' species, was thought to lock these species into a diploid or polyploid state with possible blockage of sexual reproduction. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Candida albicans」の詳細全文を読む スポンサード リンク
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