Dermatophytes

Dermatophyte literally means “skin plant” because in the 18^th century people thought that fungi were plants (silly 18^th century people). Dermatophytes cause all sorts of skin conditions from athlete’s foot to ringworm.

Case Presentation

Dermatophytes didn’t originally infect humans. They started out in the soil decomposing the hair, nails, and hooves of dead bodies. These are made of keratin (really hard to digest but dermatophytes have keratinase). Because of their origins, dermatophytes usually stay in the epidermis (it’s already dead). They actually can’t live in the dermis. In fact if they are injected into the dermis they die.

Humans have more species that affect them than any other animal. Why? Because we have lots of bare skin and live in crowded conditions with animals like cats and dogs, which give us their fungi too. There are 40 genera and 3 species of dermatophytes that affect humans, and they can be differentiated by the types of spores they produce. Macroconida have cell walls separating nuclei so they can crack into smaller units and spread out. Microconida are tiny and better at being spread around.

1. Trichophyton  only produce microconida

2. Epidermophyton  only macroconida

3. Microsporum  makes both types

Dermatophytes are also classified by where they originate:

1. Geophilic  original species, like M. gypseum and M. fulvum, causes the worst symptoms but are usually easy to get rid of, and often disapear by themselves.

2. Zoophilic  like M. canis, M. equinum, and T. mentagrophyes (rodent lover – this was a major source of discomfort for the soldiers in Vietnam).

3. Anthrophilic  T. rubrum, E. floccosum, T. violaceum (common in the Middle East), and T. tonsurans (common in the US, originated in South America and brought by Mexican migrant workers). Since these are adapted to humans they usually cause a mild disease that’s real hard to get rid of.

How do dermatophytes infect us?

Skin contact by skin flakes floating around  adhesion  form germ tube and start secreting keratins  proliferate  after 2-3 weeks the immune system kicks in and get a red lesion, sometimes you get an 'ID' reaction on chest or belly – places unconnected to site of infection.

Category: Microbiology Notes