Fungi of Medical Importance PDF

EXERCISE 9 FUNGI OF MEDICAL IMPORTANCE All fungi are heterotrophs and obtain food through absorption. They digest food externally from their body by releasing hydrolytic enzymes into other living or dead materials in the environment. The enzymes digest the food...

EXERCISE 9 FUNGI OF MEDICAL IMPORTANCE All fungi are heterotrophs and obtain food through absorption. They digest food externally from their body by releasing hydrolytic enzymes into other living or dead materials in the environment. The enzymes digest the food materials into simpler forms that the fungi can absorb and utilize. Some enzymes can also infiltrate the rigid walls of plant cells and absorb the nutrients within (Campbell et al., 2008). Fungi live in various places where there is organic matter especially in moist places. They are inhabitants not only in favorable environments but also in harsh and extreme environments like in very acidic, salty, or freezing places. They generate spores from their fruiting bodies that can germinate. The spores can also remain dormant or can resist the effects of high and low temperatures and dryness (Berg, 2012). There are three groups of fungi based on the role they perform in the environment. Many fungi act as decomposers (decomposer fungi), absorbing the nutrients from dead organic matter like the remains of plants and animals. Other fungi take up nutrients from another organism but in return benefit that organism in some ways. These fungi are called mutualistic fungi. There are also fungi that inhabit a living host’s body and feed on its cells for nutrition. These are parasitic fungi. They cause diseases and infections to the host’s body while they take in their nutrient needs. (Campbell et al., 2008). Fungal infections are termed as mycoses, which are attributed to three groups of fungi. These are the yeasts, molds, and dimorphic fungi. These fungi cause diseases through direct invasion of tissue and destruction of essential structures paired with toxic effects of the inflammatory response. Some fungi can also cause obstruction of organs which impedes flow of body fluids, or can grow in the walls of vessels causing occlusion and necrosis of tissue (Engelkirk, P. G., and Duben-Engelkirk, J., 2011). Kingdom Fungi is divided into five phyla according to their mode of sexual reproduction. The lower forms of fungi are the phylae Zygomycota and Chytridiomycota, while the higher forms are the phylae Ascomycota and Basidiomycota. The fifth phylum is the Deuteromycota, which is composed of fungi with no mode of sexual reproduction or is not known. This, this phylum is also called Fungi Imperfecti. The lower forms of fungi include the common bread molds and other fungi that cause food spoilage. The higher fungi, on the other hand, include some yeasts and fungi that cause plant diseases. Fungi Imperfecti includes molds that are medically important like the Aspergillus and Penicillium (Engelkirk, P. G., and Duben- Engelkirk, J., 2011). |1 Structure of Fungi Fungi may exist as unicellular or multicellular filaments. A common multicellular fungus is made up of filamentous structures called hyphae. These structures are bordered by tubular, chitinous cell walls and become entangled forming the mycelium, which serves as the feeding center of a fungus. The entwined structure of mycelium allows the fungus to absorb nutrients in a wider surface area (Campbell et al., 2008). Most hyphae contain walls that form across the tubes and separate the hyphae into cells. These walls are called septa. Organelles course from one cell to another through the openings of the septa. Some fungal hyphae do not contain septa that segregate cells. Inside these hyphae is a bulk of cytoplasm with lots of nuclei (Figure 10). Fungi having this kind of hypha are called coenocytic fungi (Campbell et al., 2008). Septa Pore Cell wall Cell wall Nucleus Nucleus A B Figure 1. Structure of hypha: (A) septate; (B) aseptate Lower and Higher Fungi Phylum Chitridiomycota Chytrids or chitridiomycetes dwell in many habitats. They may be observed dwelling in moist soil, ponds, and salt waters. They absorb nutrients as decomposers, or parasites (Berg, 2012), or can also be mutualists with other organisms (Campbell et al., 2008). The structure of chytrids is simple. Its body is called thallus. The thallus absorbs nutrients from the food source through its thin outgrowths called rhiziroids. The unique characteristics of chytrids is their flagellated spores (Berg, 2012) called zoospores (Campbell et al., 2008). Phylum Zygomycota Zygomycetes generate resistant sexual spores called zygospores. Each zygospore forms a thick wall that can prevent itself from drying out. It can also become dormant when faced in adverse environments for a longer time. In favorable environments, the zygospore propagates |2 and forms coenocytic hyphae. Some of the hyphae grow erect (aerial hyphae) and spore cases called sporangia are created at the apex. Each sporangium yields haploid spores that can germinate into mating types of hyphae involve in sexual reproduction (Berg, 2012). A familiar representative of zygomycetes is the Rhizopus nigricans that is commonly called as black bread molds. This species can be observed in breads and other foods with its distinctive color black spores. Its hyphae grow in few days forming mycelium and in time the aerial hyphae produce the black spores within the sporangium (Berg, 2012). Phylum Ascomycota Ascomycetes are also termed as sac fungi due to their generation of sexual spores called ascospore within saclike structures called asci. Most ascomycetes hold sexual stages in their fruiting bodies called ascocarps where the asci develop. Asexual reproduction, on the other hand occurs in the differentiated hyphae called conidiophores. The asexual spores called conidia are borne at the apex of a conidiophore. The conidia come in various colors that can be reflected in the molds formed after germination (Berg, 2012). One of the members of this phylum, the yeast, differs in structure and reproduction from other fungi. Yeasts are single-celled fungi. Their bodies are not assembled by the basic building units of most fungi, which are the hyphae. Their means of asexual reproduction is through budding and cell division. Sexual reproduction is unusual but when it happens, ascus forming four ascospores is generated (Glimn-Lacy and Kaufman, 2006). Some fungi have great importance in the medical field. One of these is the Penicillium notatum. This is an ascomycete known for its antibiotic property. This was discovered by Alexander Fleming back in 1928 (Berg, 2012) when the bacterial colonies in the culture media died after it was contaminated with Penicillium. Like other ascomycetes, asexual reproduction in this species takes place through the production of conidia (Glimn-Lacy & Kaufman, 2006). Phylum Basidiomycota The common members of this phylum are the well-known mushroom. Other members include the bracket fungi and puffballs. The mushroom is the fruiting body called basidiocarp. It contains two parts: the elongated stalk and the wide cap that is seated at the tip of the stalk. The cap contains slender plates called gills on its underside that hold club-shape structures called basidia where their name “Basidiomycetes or club fungi” originated. Each basidium generates four spores called basidiospores that are all affixed at the apex of the basidium by a stalk. The basidiospores are freed as soon as the stalk splits and can then sprout into a network of hyphae (mycelium) that contain septa. The mycelium grows subterranean and eventually produces an aerial compressed bulk of hyphae called button that becomes the basidiocarp as it grows (Berg, 2012). |3 LABORATORY ACTIVITY Learning Outcomes At the end of the exercise, the student should be able to:  identify the important parts of fungi species;  describe the physical characteristics of fungi groups;  compare the structure and characteristics of various fungi;  identify the diseases that they can cause; and  give examples of medically important species. Materials Microscope OIO oil lens paper Prepared slides: Candida albicans Penicillium sp. Rhizopus sp. Aspergillus sp. Methodology 1) Examine the prepared slides of fungi. 2) Sketch the whole structure under HPO or OIO. Label the parts of the fungi and color. HOMEWORK Answer the following in 1 whole sheet of paper. Cite five impacts of fungi to each of the following and give examples: a. Ecology b. Economy c. Medicine |4 NAME: ______________________________________________________ SCORE: _________ COURSE & GROUP #: _________________________________________ DATE: __________ EXERCISE 9 FUNGI OF MEDICAL IMPORTANCE A. Sketch the different fungi observed under the microscope. Label the parts. Phylum: ____________________________ Scientific name: ______________________ Description: _________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Magnification: __________ Phylum: ____________________________ Scientific name: ______________________ Description: _________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Magnification: __________ |5  Phylum: ____________________________ Scientific name: ______________________ Description: _________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Magnification: __________ Phylum: ____________________________ Scientific name: ______________________ Description: _________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Magnification: __________ |6  B. Complete the table below. Table 1. Diseases caused by fungi. SPECIES CATEGORY DISEASES (YEAST, MOLD, DIMORPHIC) |7