general mycology a brief review

   

In this course

introduction

history of mycology

Morphology of fungi

Growth of fungi

Metabolism of fungi

Genetics f fungi

Diseases caused by fungi

Allergies

Mycosis

Mycotoxin

Laboratory diagnosis of fungi

Antifungal Drugs used in treatment fungal diseases

       

HISTORY OF THE SCIENCE

The term “mycology” is derived from Greek word “mykes” meaning mushroom.     Therefore mycology is the study of fungi The ability of fungi to invade plant and animal tissue was observed in early 19th century but the first documented animal infection by any fungus was made by Augastino Bassi , who in 1835 studied the muscardine disease of silkworm proved that the infection was caused by a fungus Beauveria bassiana. Remark, who found the fungal nature of favus in 1837 Berg who reported oral candidiasis in 1841 Wilkinson, who described vaginal candidiasis in 1849. Tinea versicolor was described clinically in 1846 by Eichstaedt, and its etiologic agent was identified in 1853. Beigel reported white Piedra in 1856 Piedra, which means “stone” in Spanish, is an asymptomatic superficial fungal infection of the hair shaft. In 1865, Beigel first described Piedra in The Human Hair: Its Structure, Growth, Diseases, and Their Treatment; although, he may have been describing Aspergillus infection. Cerqueira, tinea nigra in 1891 In 1910 Raymond Sabouraud published his book Les Teignes, which was a comprehensive study of dermatophytic fungi. He is also regarded as father of medical mycology. In 1927, Nan Nizzi reported the description of the sexual state of Microspore gypsum. In 1927, Nannizzi reported the description of the sexual state of Microsporum gypseum the taxonomy of yeast fungi was described by Lodder and Kregervan Rij in 1952. The current classification of dermatophytes was published by Emmons in 1934 Finally, Gentles’ successful treatment of tinea capitis with griseofulvin by in 1958 saved many patients with tinea capitis from permanent hair loss a common side effect after treatment with thallium importance of fungi Fungi inhabit almost every niche in the environment and humans are exposed to these organisms in various fields of life.

Harmful Effects of Fungi:

1. Destruction of food, lumber, paper, and cloth. 2. Animal and human diseases, including allergies . 3. Toxins produced by poisonous mushrooms and within food (Mycelium and Mycotoxicosis) . 4. Plant diseases. 5. Spoilage of agriculture produce such as vegetables and cereals in the godown. 6. Damage the products such as magnetic tapes and disks, glass lenses, marble statues, bones and wax.

Beneficial Effects of Fungi: 1. Decomposition

nutrient and carbon recycling .

2. Biosynthetic factories.

The fermentation property is used for the industrial production of alcohols, fats, citric, oxalic and gluconic acids. 3. Important sources of antibiotics, such as Penicillin.

4. Model organisms for biochemical and genetic studies

. Eg: Neurospora crassa

5. Saccharomyces cerviciae is extensively used in recombinant DNA technology, which includes the Hepatitis B Vaccine

. 6. Some fungi are edible (mushrooms).

7. Yeasts provide nutritional supplements such as vitamins and cofactors.

8. Penicillium is used to flavour Roquefort and Camembert cheeses.

9. Ergot produced by Claviceps purpurea contains medically important alkaloids that help in inducing uterine contractions, controlling bleeding and treating migraine. 10. Fungi (Leptolegnia caudate and Aphanomyces laevis) are used to trap mosquito larvae in paddy fields and thus help in malaria control.

Notice Fungi are eukaryotethey have true nuclei surrounded by nuclear membrane and have rigid cell wall like plant they are larger than prokaryote with typically filamentous growth the majority are aerobes they require oxygen at some stage of their growth

Fungi live every whereand have very diverse habitat most fungi are saprophytes and found on vegetation decomposing organic matter soil and waters some are parasite on plants animals and insects Many fungi can produce mycotoxin in food and in animal feeds which can cause toxicosis some used in food industries saccharomyces used in alcoholic drink yoghurt bread penicillium Roquefort which is used in producing cheese many used in vitamins production penicillium chryogenium used in producing pencillin G some are obligate aerobes others facultative aerobes and can ferment sugar and grow anaerobically fungi are organotrophs require organic source of carbon fungi are slow grower in comparison to many bacteria and resistant to antibiotics

Fungi grow in two morphologic forms yeasts or molds Yeast form yeasts grow mainly by budding producing spherical to ellipsoidal cells 3-15 micron in diameter either single or attached to each other forming pseudo hyphae they never produce aerial hyphae this is reflected on morphology of colonies on agar media which resemble bacterial growth the colony are pasty opaque and may be white creamy yellowish red or even black in color the yeast color generally attain a diameter of 0.5- -3 mm within 3 days the mould form the mould grow through the development of tube like extension forming what is known as hypha the mass of interwind hyphae is called mycelium the hypha may be divided into individual cells by septa which is cross walled that present one or two pores The hypha may present no septa and remain as continuous tube apportion of mycelium grows into the medium called vegetative mycelium visible part grow above the medium called aerial mycelium The aerial mycelium gives the colony fluffy appearance and bear the reproductive structures which give the colony its color The mold colony varies in its appearance size from few mm to few cm so the single colony may cover all the surface of the plate it may be Glabrous verrucose fluffy surface texture may be velvety cottony powdery may assume any color or grade of color known in nature Some molds have the character of dimorphism dimorphic moulds as they can grow also in a yeast form it takes place in tissue when the mold invade tissues it change to yeast form or In lab when the colony plated on enriched media such as brain heart infusion agar and incubated at 37c The rigid cell wall of fungi consisted of chitinous microfibrils embedded in a matrix of small polysaccharides protein lipids the major polysaccharide cell wall matrix consisted of glucan, manans, chitosan and galactan Yeasts have soluble peptidomanans as component of their outer cell wall the outer cell wall of dermatophytes contains glycopeptides that may evoke both immediate and delayed hypersensitivity The plasma membrane is similar to the mammalian plasma membrane differ it has the non polar ergosterol instead of cholesterol as a principal sterol this is the site of action of antifungal Fungal nuclei are variable in size and shape and numbers the DNA and associated protein occur as long filaments of chromatin which condense during nuclear division the number of chromosomes varies with particular fungus the fungal cell may contain up to 100 mitochondria

Growth of fungifungi need for their growth a source of carbon e.g sugar a source of nitrogen e.g peptone inorganic compound as ammonium nitrate and source of inorganic nutrients potassium phosphorous magnesium Water is an absolute requirement for fungi fungi are more tolerant for water stress than other organisms but in draught no growth occur spore can survive in a suitable medium the fungal spores germinate forming germ tubes which develop into hyphae Growth temperature of fungi mesophilic between 10- 40C optimum temperature 25-35C some fungi grow best at 37 C Thermophilic or Thermotolerant they grow at temperature between 20-and 60 C with optimum of 40C Psychrophilic fungi grow at low temperature that reach to-20 as molds which grow on frozen meat e.g. Cladosporium The optimum PH of fungi is in the range 56-6.5 while few fungi grow below ph3 or aboveph9 several acidophilic fungi grow at pH 2 e.g. Aspergillus and penicillium few fungi are basophilic can grow at 10-11 e.g. fusarium exosporium   metabolism of fungi  Metabolism of fungi fungi preferer moist habitat they are heterophilic need carbon in soluble form of carbohydrate as carbon in environment is found as complex polymer they use their own enzyme like cellulase chitinase in degrading cellulose lignin Fungi cannot fix gaseous nitrogen but they can utilize nitrate ammonia some amino acids by direct uptake by hyphal membrane they can utilize more complex nitrogen sources such as protein and peptides as they can utilize extracellular proteases that degrade amino acids into amino acids Fungi require macro and micronutrients sometimes vitamins fungal genetic  atypical model for studing genetic saccharomyces serviceae 

diseases caused by fungi

allergies

mycosis 

mycotoxin

lab diagnosis of fungal diseases

  antifungal  Drug used in treating fungal diseases

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