Filamentous fungi consist of unicellular, thread-like hyphae that can form webs by branching. Of the many existing species of filamentous fungi, pathogenic skin fungi and, indirectly, molds are of primary health relevance to humans. Certain molds of the genus Penicillium, which occur in soil and on plants, synthesize the antibiotic penicillin, while other species are needed, for example, in the production of certain types of cheese.
What are filamentous fungi?
The phenotypic characteristic of filamentous fungi is their thread-like cells, called hyphae, which can branch and each has a nucleus. Because filamentous fungi rely on organic material for their nutrition and their cells have a nucleus, they are heterotrophic eukaryotes (also called eukaryotes). The hyphae of the evolutionarily younger filamentous fungi have partition walls (septa) that make targeted transport of material possible. Evolutionarily older filamentous fungi do not develop septa in their hyphae. Reproduction of filamentous fungi occurs through the formation of sexual or asexual spores, from which new filamentous fungi are formed. From the multitude of different species of filamentous fungi, especially the skin fungi (dermatophytes) have direct health relevance for humans, while other species have only indirect relevance for humans through their synthesized substances. These are certain poisons, called mycotoxins, such as aflatoxin, or antibiotic substances such as penicillin. Some filamentous fungi are needed in the production of certain cheeses.
Occurrence, distribution, and characteristics
Filamentous fungi are found almost ubiquitously on nearly all organic substrates. The vast majority of species of filamentous fungi have no direct health relevance to humans, but they do to most plants and trees capable of photosynthesis. The hyphae of many species form symbiotic relationships with the roots of trees and other plants, so-called mycorrhizae. They are of enormous importance to forests, for example, for growth, hardiness, and drought resistance. The overall importance of mycorrhizae to the plant community is not yet sufficiently understood scientifically. Filamentous fungi with direct health, pathogenic relevance are the skin fungi, also called dermatophytes. They each belong to one of the three genera Microsporum, Trichophyton or Epidermophyton (of which Epidermophyton floccosum is human pathogenic). Dermatophytes are characterized by the fact that, in the case of infection of the skin, they not only require carbohydrates from the body, but can also “digest” the keratin of dead skin cells, as they possess the enzyme keratinase. A fungal infection of the skin (dermatophytosis or tinea) ranges in terms of clinical picture from relatively harmless to severe or even, in rare cases, life-threatening. Symptomatic are reddening of the skin at the infected sites, which may ooze or ulcerate and are usually associated with severe itching. Particularly susceptible to infection are areas of the body where the skin is kept warm and moist, such as between the toes. Skin fungus is contagious via direct contact. Predestined for infection are public baths and saunas.
Meaning and function
Indirect health significance is provided by certain types of molds that synthesize antibiotics such as penicillin. The mold Penicillium chrysogenum is still the best-known supplier of antibiotics today. However, many antibiotics are now produced synthetically. Antibiotics interfere with various metabolic processes of certain bacteria and thus have a bacteriostatic or bacteriocidal effect. When using antibiotics, two problem areas must be considered in each case. On the one hand, antibiotics do not have a very specific effect. This means that in addition to the pathogenic bacteria that are to be killed by the antibiotic, beneficial bacteria – especially in the digestive tract – are also attacked. The other difficulty is multiresistance, which can develop in pathogenic bacteria as a result of gene mutation when the particular strain of bacteria is frequently exposed to antibiotics and a positive survival selection automatically develops in the bacteria, which manifests itself as multiresistance.Filamentous fungi, which are required for the production of certain foods such as blue cheese, also have an indirect significance for the body and health. As a rule, the mold Penicillium roqueforti is added, which gives the cheese its characteristically pungent taste and produces visible blue mold nests in the cheese. However, Penicillium roqueforti lives aerobically, so the cheese mass is pricked with thin needles to ensure the presence of oxygen. Filamentous fungi are also used in beer and wine production and for many fermentation processes.
Diseases and ailments
The greatest direct threat to humans comes from infection with a dermatophyte, although an intact and unsuppressed immune system fights the filamentous fungi early enough to produce only mild or no symptoms. The two fungal species that account for over 90 percent of all fungal skin infections are Trichophyton rubrum, which mainly attacks skin areas, and Trichophyton mentagrophytes, which prefers to attach to hair roots and the sites where hair exits the skin. Circulatory disorders and diabetes mellitus, as well as AIDS, for example, favor infection with dermatophytes. In rare cases, when the skin fungus is confronted with an extremely weakened or artificially suppressed immune system to avoid defense reactions, the fungus can overcome skin or mucous membranes and spread systemically through the bloodstream and infect internal organs. In very rare cases, it can even infect the brain, which is associated with a life-threatening risk. In individuals who frequently suffer from fungal skin infections, genetic causes may also play a role if a family history of fungal infections can be identified.
