Microsporum nanum
From Wikipedia, the free encyclopedia
| Microsporum nanum | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Onygenales |
| Family: | Arthrodermataceae |
| Genus: | Microsporum |
| Species: | M. nanum |
| Binomial name | |
| Microsporum nanum C.A.Fuentes (1956) | |
| Synonyms | |
| |
Microsporum nanum is a pathogenic fungus in the family Arthrodermataceae. It is a type of dermatophyte that causes infection in dead keratinized tissues such as skin, hair, and nails.[1][2] Microsporum nanum is found worldwide and is both zoophilic and geophilic. Animals such as pigs and sheep are the natural hosts for the fungus; however, infection of humans is also possible. Majority of the human cases reported are associated with pig farming. The fungus can invade the skin of the host; if it is scratched off by the infected animal, the fungus is still capable of reproducing in soil.[3]
When grown on Sabouraud's Dextrose agar at 25 °C, M. nanum produces a thin, powdery, and soft fibrous colony that appears white at the center becoming light yellowish-brown towards the colony margin. The reverse side appears brownish-orange in young colony and reddish-brown in older colony.[4][5] The mitochondrial genome of M. nanum consists of 15 protein-coding genes, 2 rRNAs, 25 tRNAs, one intron and one intronic ORF. Approximately 84% of the mitochondrial genome are the structural genes.[6] Microsporum nanum infections include tinea capitis, tinea corporis, tinea cruris, and tinea faciei.[3] Griseofulvin, clotrimazole, miconazole,[7] enilconazole[8] and many herbal treatments, such as extracts from Azadirachta indica,[9] essential oil from Curcuma longa[10] and Eucalyptus pauciflora[11] have been reported to be effective in inhibiting the fungus.
Microsporum nanum was first thought to be a variant of M. gypseum by Fuentes, Aboulafia, and Vidal who named it M. gypseum var. nanum in 1954.[12] Significant morphological differences between the macroconidia of M. gypseum var. nanum and M. gypseum var. gypseum prompted Fuentes to elevate the former to the species-level as M. nanum two years later.[13] The sexual reproductive (teleomorph) stage of M. nanum was first described by Dawson and Gentles as Nannizzia obtusa in 1961 who isolated it from skin lesions in pigs in Kenya.[14] The name was changed to Arthroderma obtusum by Weitzman, McGinnis, Padhye and Ajello in 1986.[15]
Description
Microsporum nanum is a mesophile and grows moderately rapid on Sabouraud's Dextrose agar. Its macroconidia are ovoid in shape and, unlike those of most other species of Microsporum, normally consist of no more than three cells. Rare to moderate numbers of rough-walled microconidia can also be found in the colony.[3] Microsporum nanum grows optimally at 25 °C but is capable of growth at temperatures up to 37 °C. Physiological tests have shown that M. nanum does not require vitamin supplementation for its growth. Like many other dermatophytes, M. nanum is tolerant of the antifungal agent cycloheximide. In addition, M. nanum also exhibits soil association characters such as urease activity and the formation of perforating organ on hair shafts.[16]
Mitochondrial genome
Mitochondrial DNA sequences have been used for phylogenetic studies in the dermatophytes. A typical fungal mitochondrial DNA usually contains 14 conserved protein-coding genes, 22 to 26 tRNA gene, and 2 rRNA genes. The difference of mitochondrial DNA between fungal species is due to the variations in intergenic region, intron, and gene order. The complete sequences of Trichophyton rubrum, T. mentagrophytes, T. ajelloi, M. canis, M. nanum, and Epidermophyton floccosum show that these 6 species in dermatophytes are closely related because their mitochondrial genomes are highly conserved. Genome size of mitochondrial DNA in M. nanum is 24,105 basepairs. The DNA is AT-rich and the GC content is only 24.47%. M. nanum mtDNA has 15 protein-coding genes, including ATP synthase subunits atp6, atp8, and atp9, cytochrome oxidase subunits cox1, cox2, and cox3, apocytochrome b cob, a ribosomal protein rps5, and NADH dehydrogenase subunits nad1, nad2, nad3, nad4, nad5, and nad6. The gene order of the 15 conserved protein coding genes in M. nanum mtDNA is identical to that of T. rubrum, T. mentagrophytes, T. ajelloi, and M. canis. The Microsporum nanum mtDNA also contains 2 rRNAs and 25 tRNAs. In addition, this mitochondrial genome is highly compact because 83.76% are structural genes. Moreover, the genome contains one intron and one intronic ORF.[6]