Microsporum canis
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| Microsporum canis |
Description and significance
Microsporum canis is a fungus also known as a dermatophyte that causes dermatophytosis (ringworm) in canines and felines. They are commonly found in humid, warm climates. Although canines and felines are its natural reservoir it can cause ringworm in humans.
Genome structure
Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?
Cell structure and metabolism
Microscopically this species has multicelled macroconidia (spores) with thick, rough walls. They are barreled shaped with an asymmetrical apical knob and are 6 to 15 cells long. When grown on a culture medium for at least 4 days colonies produce a white cottony surface with yellow around the periphery and the underside is bright yellow or orange. (2) This organism gains energy from keratin found in nails, hair and skin. It secretes keratinolytic protease, which provides the fungus with nutrients by degrading keratin into easily assimilable metabolites. This secreted protease also allows the invasion of keratinized structures and controls the host defense mechanisms. (4)
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
This fungal pathogen causes ringworm mainly in cats and dogs, but is a common source for human infection. This fungus can be picked up by direct contact with other infected animals or by contact with spores that have contaminated objects such as grooming equipment, furniture and the environment. Spores are very resistant without treatment and can live up to two years infecting animals and humans. Spores will attach to the skin and germinate producing hyphae, which will then grow in the dead, superficial layers of the skin, hair or nails. The most investigated virulence factors has been keratinolytic protease. The secretion of this protease causes some damage to the skin and hair follicle. The skin will have a hypersensitive reaction becoming inflamed causing the fungus to move away from the site to normal skin. This creates characteristic circular lesions with healing at the center and inflammation at the edge. (3) Some cats can be asymptomatic while others will exhibit flacky skin, hair lose and occasionally inflamed skin. Cats that are less than a year old, long haired or have a comprised immune system are more susceptible to ringworm. A reason for younger cats susceptibility to this fungus can be that their immune system is immature and its defense mechanisms are limited to infection. Long haired cats are easier targets for infection because their grooming is less efficient and self grooming is an effective way of removing spores from the skin and fur. Their long hair also protects the dermatophytes from sun exposure which they can not tolerate. The infection is primarily found on ears head or extremity of the paws. Dogs will exhibit non-inflammatory flaky skin with hair lose.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
Microsporum canis is a parasitic fungus that secretes keratinolytic protease to invade keratinized structures of hair, skin and nails in humans and animals. They cause dermatophytosis in mainly dogs and cats, but human infections are increasing, especially in many European countries. A reason for increased infections in humans is due to asymptomatic infected cats.
Most research has been conducted on keratinolytic protease, which is secreted by this fungus. There is evidence of it being a potential virulence factor by controlling the host’s defense mechanisms. Keratinolytic protease also provides the fungus nutrients by degrading keratin structures into easily absorbable metabolites.
M. canis secretes a keratinolytic subtilisin-like protease called 31.5 kDa. It also secretes three subtilisin-like proteases (SUBs), SUB1, SUB2 and SUB3. An in vitro expression of this protease has been studied much more than the in vivo expression. The isolation and characterization of these three SUBs allow for the study of their potential role of pathogenesis of M. canis dermatophytosis in the in vivo transcription of their genes, which is demonstrated in the hair of experimentally infected guinea pigs.
The detection of the in vivo transcription of SUB1, SUB2, and SUB3 was seen on agarose gel as bands. This was not detected under the same conditions in control extracts. Obtaining RT-nested PCR products, from total RNA extracted of M. canis infected hair of guinea pigs allowed for this procedure. The results revealed homology between SUB1, SUB2, and SUB3 by the identification of the catalytic triad, conserved residues typical of serine proteases of the subtilisin family and by the high amino acid identity percentage. This suggests that M. canis contains a family of SUBs. Proteases encoded by a gene family have been shown to be related to virulence in other fungal infections and this would be evidence of M. canis pathogenic infection. The article states that further research needs to be conducted on the fungal infection of M. canis.
References
1) http://www.fabcats.org/owners/skin/ringworm.html
2) http://www.doctorfungus.org/thefungi/microsporum_canis.htm 3)http://www.vetstreamfelis.com/ACI/January08/VMD1/bug00270.asp
4)http://www.nature.com/jid/journal/v119/n4/full/5601629a.html#bib23