language-icon Old Web
English
Sign In

Candida albicans

Candida albicans is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usually a commensal organism, but it can become pathogenic in immunocompromised individuals under a variety of conditions. It is one of the few species of the genus Candida that causes the human infection candidiasis, which results from an overgrowth of the fungus. Candidiasis is for example often observed in HIV-infected patients.C. albicans is the most common fungal species isolated from biofilms either formed on (permanent) implanted medical devices or on human tissue. C. albicans, C. tropicalis, C. parapsilosis, and C. glabrata are together responsible for 50–90% of all cases of candidiasis in humans. A mortality rate of 40% has been reported for patients with systemic candidiasis due to C. albicans. By one estimate, invasive candidiasis contracted in a hospital causes 2,800 to 11,200 deaths yearly in the US. Nevertheless, these numbers may not truly reflect the true extent of damage this organism causes, given new studies indicating that C. albicans can cross the blood brain barrier. C. albicans is commonly used as a model organism for biology. It is generally referred to as a dimorphic fungus since it grows both as yeast and filamentous cells. However, it has several different morphological phenotypes. C. albicans was for a long time considered an obligate diploid organism without a haploid stage. This is, however, not the case. Next to a haploid stage C. albicans can also exist in a tetraploid stage. The latter is formed when diploid C. albicans cells mate when they are in the opaque form. The diploid genome size is approximately 29 Mb, and up to 70% of the protein coding genes have not yet been characterized.C. albicans is easily cultured in the lab and can be studied both in vivo and in vitro. Depending on the media different studies can be done as the media influences the morphological state of C. albicans. A special type of medium is CHROMagar™ Candida, which can be used to identify different species of candida. Candida albicans can be seen as a tautology. Candida comes from the Latin word candidus, meaning white. Albicans itself is the present participle of the Latin word albicō, meaning becoming white. This leads to white becoming white, making it a tautology. It is often shortly referred to as thrush, candidiasis, or candida.More than a hundred synonyms have been used to describe C. albicans.Over 200 species have been described within the candida genus. The oldest reference to thrush, most likely caused by C. albicans, dates back to 400 BCE in Hippocrates' work Of the Epidemics describing oral candidiasis. The genome of C. albicans is almost 16Mb for the haploid size (28Mb for the diploid stage) and consists of 8 sets of chromosome pairs called chr1A, chr2A, chr3A, chr4A, chr5A, chr6A, chr7A and chrRA. The second set (C. albicans is diploid) has similar names but with a B at the end. Chr1B, chr2B, ... and chrRB. The whole genome contains 6,198 open reading frames (ORFs). Seventy percent of these ORFs have not yet been characterized. The whole genome has been sequenced making it one of the first fungi to be completely sequenced (next to Saccharomyces cerevisiae and Schizosaccharomyces pombe). All open reading frames (ORFs) are also available in Gateway-adapted vectors. Next to this ORFeome there is also the availability of a GRACE (gene replacement and conditional expression) library to study essential genes in the genome of C. albicans. The most commonly used strains to study C. albicans are the WO-1 and SC5314 strains. The WO-1 strain is known to switch between white-opaque form with higher frequency while the SC5314 strain is the strain used for gene sequence reference. One of the most important features of the C. albicans genome is the high heterozygosity. At the base of this heterozygosity lies the occurrence of numeric and structural chromosomal rearrangements and changes as means of generating genetic diversity by chromosome length polymorphisms (contraction/expansion of repeats), reciprocal translocations, chromosome deletions, Nonsynonymous single-nucleotide polymorphisms and trisomy of individual chromosomes. These karyotypic alterations lead to changes in the phenotype, which is an adaptation strategy of this fungus. These mechanisms are further being explored with the availability of the complete analysis of the C. albicans genome. An unusual feature of the genus Candida 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. However, this different codon usage makes it more difficult to study C. albicans protein-protein interactions in the model organism S. cerevisiae. To overcome this problem a C. albicans specific two-hybrid system was developed. The genome of C. albicans is highly dynamic, contributed by the different CUG translation, 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 redefinition, occurring in ancestors of Candida species, was thought to lock these species into a diploid or polyploid state with possible blockage of sexual reproduction.

[ "Genetics", "Biochemistry", "Botany", "Microbiology", "Immunology", "Candida granuloma", "Yeast form", "Corpus albicans", "Denture fitting", "Denture lining material" ]
Parent Topic
Child Topic
    No Parent Topic