What is it? Classification, in Medicine and How to Culture
Definition: What is Mycology?
Essentially, mycology is the study of fungi. Here, mycologists directly focus on the taxonomy, genetics, application as well as many other characteristics of this group of organisms.
Currently, over 50,000 species of fungi have been identified in different environments across the globe. While some are free-living and have no impact on human beings (and other animals), some are either beneficial or harmful making it necessary to study and understand them.
This has not only made it possible to develop treatments for diseases caused by specific species of fungi, but also use certain species in a variety of industries (pharmaceutical, food, agriculture and alcohol among others).
Currently, fungi described as "true fungi" under the fungi kingdom are grouped into several phyla.
Based on Sexual Reproduction:
· Blastocladiomycota- Members of this phylum are either parasite of plants and animals or saprotrophs. They can be found in both aquatic and terrestrial environments and produce spores that go through meiosis.
· Neocallimastigomycota- Most of the fungi in this group are anaerobic in nature. They can be found in the digestive tract of large herbivores and zoospores move through the use of flagella.
· Glomeromycota- Members of this phylum form a symbiotic relationship with various plants and trees. As such, they are not necessarily parasites that fully depend on the host. The majority of the species reproduce asexually.
· Zygomycota- This is a relatively small group made up of organisms that are referred to as saprobes. As such, they largely depend on decaying organic material as the source of energy.
A few species, however, are parasitic in nature. Zygomycetes reproduce asexually and produce zygospores. Although species like R. stolonifer obtain their energy from decaying matter (e.g bread) they cause food spoilage and can cause diseases.
· Basidiomycota- Known as club fungi, this phylum is largely composed of mushrooms, smut fungi, and rust. The majority of basidiomycetes are pathogens of grains and tend to produce sexually. Spores of basidiomycetes are referred to as basidiospores.
· Ascomycota- Also known as sac fungi, members of Ascomycota include mushrooms, yeast, truffles, and morels. A majority are filamentous that either exist as parasites or saprophytes. However, they can also form symbiotic relationships with other organisms. They produce sexually and asexually.
· Chytridiomycota- Members of this group are also known as chytrids and produce spores known as zoospores. In aquatic environments, these organisms move using a flagellum and reproduce asexually.
Apart from classification based on the mode of reproduction, fungi are also classified based on the following aspects:
With regards to morphology, fungi are classified as either molds or yeast.
Mold Fungi (Filamentous/Hyphal)
Molds are a group of fungi that are filamentous in nature. As such, they produce hyphal threads that form a mass known as mycelium (vegetative, aerial or fertile). Depending on the species, the hyphae may be branched or have septums.
Unlike moulds/molds, yeast are unicellular that may vary from spherical to ellipsoid in shape.
Yeast are further divided into:
True yeast - cells that reproduce through budding (e.g. S. cerviciae)
Yeast-like fungi- Cells that produce false hyphae known as pseudohyphae (E.g. C. neoformans)
Dimorphic fungi- Depending on the environment, dimorphic fungi can exist in two forms (mold or yeast)- E.g. P. marneffei
According to mycology studies, some groups of fungi have been shown to be restricted to specific geographic regions. It has been shown that while fungi species are distributed across the globe, their diversity in different regions are influenced by such factors as soil chemistry and the climate among others. For this reason, different species of fungi can be associated with certain geographical locations.
Epidemiologic grouping is one of the classification methods used in medical mycology. This has allowed for the identification and characterization of a variety of invasive fungi.
Here, some of the most common species have included members of Aspergillus, Candida, Cryptococcus, and Pneumocystis among others. This approach has also been used to differentiate invasive and non-invasive fungi.
For instance, fungal rhinosinusitis is divided into invasive and non-invasive depending on how the fungi invade the mucosal layer. While this is non-invasive in some cases (where the fungus only occupies the surface of the mucosal layer) there are cases where the fungi invade this layer.
Like geographic grouping, then, epidemiologic grouping can be used to classify groups of fungi based on how given fungi affects human beings.
Mycology is a wide field of study that is divided into several branches. This includes such divisions as forensic mycology, Ethnolichenology, and lichenology among others. These divisions allow mycologists to focus on specific areas of the field.
In the food and alcohol industry, for instance, focus is directed towards the use of certain fungi for food production (yogurt etc) fermentation and food preservation etc. Medical mycology, on the other hand, is concerned with the study of fungal infections in human beings.
While fungal infections observed on the skin, hair, and nail may not have serious health implications, some fungal infections can prove serious particularly among those with weakened immune system.
For this reason, the characteristics and modes of infection of fungi are areas of great significance in medical mycology. Given that medical mycology is focused on fungi infections, it is also closely associated with such medical fields as toxicology, dermatology, and immunology among others.
In mycology, culture techniques are used to grow and study various characteristics of a fungus. Although it is relatively easy to culture fungi, a lot of care is required in such fields as medical mycology. This is due to the fact contamination can easily occur affecting the quality of results.
General knowledge regarding aseptic techniques, media preparation, sterilization, and transfer methods, etc, is important to obtain meaningful results.
This section will focus on two major techniques used for the culture of yeast and mold fungi.
Culture medium - Sabouraud’s Dextrose agar which is an isolation medium
Before starting the actual procedure, it is important to ensure that all material used are clean and sterilized. Although an isolation medium is used for this technique, this is an important step in all culture protocols.
Sample collection and preparation
· The sample (C. albicans) may simply be obtained using a clean cotton swab. Here, a clean cotton swab is used to collect the yeast from the mouth of an infected individual. The collection may also involve the oral rinse technique. Here, the individual holds phosphate-buffered saline (about 10mL) in his/her mouth for a minute. This is then concentrated using a centrifuge to obtain a good sample.
· Pour the culture medium (SDA ) onto a clean Petri dish
· Using a sterile wire loop of the cotton swab, inoculate the sample on the agar medium using the spiral plating system
· Incubate the culture at 37 degrees Celsius for about one to two days
After two days of incubation, colonies of the yeast (C. albicans) are characterized by a smooth, creamy complex.
Mold Fungus: Aspergillus Flavus
Aspergillus flavus is a mold that is known to colonize grains and various plants.
Spore sample - Conidium of the fungus
Potato Dextrose Agar (PDA) - Medium
Cotton swab/wire loop
The fungal sample for this procedure may be obtained from poultry feed samples
Using a sterile cotton swab or wire loop, inoculate the conidial suspension on to the agar medium (PD) in the petri dish
Incubate the plate at 25 degrees Celsius for about 7 days in the dark
After 7 days of incubation, Aspergillus flavus will appear dark brown/green in color. A closer view of the plate also reveals radial mycelial growth.
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