Introduction to mycology Flashcards
What is mycology?
The study of fungi
What is mycoses?
A Fungal infection
What kind of growth do molds exhibit?
They exhibit filamentous type of growth.
What kind of functional growth do yeasts exhibit?
Do fungi stain gram positive or negative?
Do they require oxygen to survive?
- Exhibit pasty or mucoid form of fungal growth- grow as single cells (colonies)
- Fungi stain gram positive, and require oxygen to survive
Fungi are eukaryotic, containing:
- Nucleus bound by a membrane
- Endoplasmic reticulum
- Mitochondria.
- Rigid cell wall- chitin (directly above phospholipid bilayer) and glucans (criss-cross network of beta 1,3 and others that are embedded)
- Glycoproteins are also within that matrix
- Yeasts have ergosterol instead of cholesterol
What are the main properties of fungi and what is their main source of energy?
Fungi are heterotrophic like animals and most bacteria; requiring organic nutrients as a source of energy
Are fungi closer to animal or plants?
Describe Yeast reproduction:
Describe the process of budding
- Reproduce either asexually or sexually dependent on the nutrients in their environment
- Sexual reproduction (if any) through meiosis results in the formation of the appropriate spore structure
- Asexual reproduction is through budding* or binary fission:
- The parent cell is seen outgrowing a small bud like structure (protuberance)
- The nucleus of the parent cell is seen divided into two parts.
- The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell
- The size of the bud increases and simultaneously so does the size of the nucleus.
- The bud grows as large as the parent cell
- The bud detaches from the mother’s body by forming a constriction at the base
- Budding will repeat to form a chain of bud cells. The daughter cell produced during the budding process is generally smaller than the mother cell
Yeasts vs molds
Describe the classification of fungi
From the diagram:
- True fungi listed on the left of the diagram
- Straminipila are algae that form on the water surface (not true fungi)
- Slime molds can live freely as single cells, but can aggregate together to form multicellular reproductive structures. Were formerly classified as fungi but are no longer considered part of that kingdom
Ascomycota
- Its members are commonly known as the sac fungi or ascomycetes
- Discovered over 300 million years ago
- The defining feature of this fungal group is the ascus →microscopic structures containing sexual ascospores
- Microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle and thus do not form asci or ascospores
- 75% of fungal population
- Largest phylum of the fungi with over 64,000 species:
- Examples of ascomycetes that can cause infections in humans include Candida albicans, Aspergillus niger, penicillium species and several tens of species that cause skin infections.
- True yeasts:
- Saccharomyces*
- Candida*
Ascomycota:
What are ascopores?
Where does nuclear fusion and meiosis take place?
Asexual reproduction takes place via:
- They are called ‘sac fungi’ because their sexual spores called ascospores are produced in a sac or ascus
- In other words sexual reproduction in the Ascomycota leads to the formation of the ascus, the structure that defines this fungal group and distinguishes it from other fungal phyla
- Nuclear fusion and meiosis take place within the ascus.
- Ascomycota have more than one reproductive option;
- Asexual reproduction takes place via conidiospores (meitospores):
Two unrelated cells conjugate (in nutrient rich media) to form a diploid bud (contains genetic information from both cells) then 4 haploid ascopres form via meiosis and are surrounded by an ascus sac
What are zygomycota?
- They are mostly terrestrial in habitat, living in soil or on decaying plant or animal material.
- Form spherical spores during sexual reproduction
- The mycelia (vegetative part of a fungus, consisting of a network of fine white filaments (hyphae) of Zygomycota are divided into three types of hyphae.
From the fist diagram:
- The rhizoids reach below the surface and function in food absorption.
- Above the surface, sporangiophores (formed asxually) bear the spore-producing sporangia. These specialized hyphae usually show negative gravitropism and positive phototropism allowing good spore dispersal.
- Stolons connect Rhizoids and sporangiophores above the surface.
Basidiomycota:
What are their properties?
- Filamentous fungi composed of hyphae, reproducing sexually through specialised basidia.
- Includes mushrooms, puffballs, brackets, yeasts
- Microscopic fungi, inc rust fungi and smut fungi that parasitise plants
- Sporobolomyces roseus, common on moribund leaf surfacesbasidiospores are respiratory allergens.
- Cryptococcus neoformans, grows on old “weathered” bird droppings causes fatal systemic infection Its air-borne basidiospores initiate infection via the lungs, leading to the disease termed cryptococcosis.
- Commercially grown for food, including the common cultivated mushroom
Explain the role of fungi in the economy
- Mushrooms. (Class Basidiomycetes)
- Truffles. (Class Ascomycetes)
- Natural food supply for wild animals.
- Yeast as food supplement, supplies vitamins.
- Penicillium - ripens cheese, adds flavor (roquefort, etc.)
- Fungi used to alter texture, improve flavour of natural and processed foods
Fermentation
Saccharomyces cerevisiae - brewer’s and baker’s yeast.
Yeast + Glucose = Alcohol (Ethanol) + CO2
In bread desired product is then the carbon dioxide which helps the bread rise
In fizzy drinks the desired product is also carbon dioxide
Penicillin: the story of an antibiotic 1929
- The antibacterial effect of penicillin was discovered by Alexander Fleming in 1929.
- Fungal contaminant on an agar plate streaked with the bacterium Staphylococcus aureus
- Before leaving for his holiday, he had stacked all his cultures of staphylococci on a bench in a corner of his laboratory. On returning, Fleming noticed that one culture was contaminated with a fungus, and that the colonies of staphylococci immediately surrounding the fungus had been destroyed, whereas other staphylococci colonies farther away were normal,
- Fungal metabolite that might be used to control bacteria.
- The substance was named penicillin: fungal contaminant was identified as Penicillium notatum.
- Fleming found that it was effective against many
Common Fungal Pathogens
- Most fungi grow in nature as saprophytes on dead organic material and obtain nutrients directly from dead organic matter or waste; important catalysts in the carbon cycle.
- Parasites- live on living organisms
- Important in medicine as both agents of disease and in chemotherapy (antibiotic production).
- Only 50 species of fungi cause human diseases. Systemic infection in immuno-compromised individuals
Disease caused by fungi
- Athletes foot
- Thrush
- Lung infections
Athletes foot
- Athlete’s foot (tinea pedis) of the skin of the foot
- Parasitic
- Trichophyton mentagrophytes
appears suddenly
Severe
easily treated.
- Trichophyton rubrum
often causes moccasintype (scaly) infections.
lasts for a long time (chronic)
difficult to treat
What are the symptoms of athletes foot?
- Toe web infection (interdigital)
Peeling, cracking, and scaling of the feet.
Redness, blisters, or skin softening
Itching, burning
- Moccasin-type infection
long-lasting (chronic) infection.
Sever: toenails become infected and can thicken, crumble & even fall out
Diagnosis in the lab
- Sample sent to be cultured (skin scraping/toe nail)
- Portions of the nail specimen were placed on SAB (Sabouraud) agar (and Mycocel media for isolation). It is used to cultivate dermatophytes and other types of fungi
- Portion may be flooded with 10% KOH
Compositiion:
Mycological peptone 10.0g/L
Glucose (dextrose) 40.0g/L
Agar 15.0g/L
pH 5.6 ± 0.2 at 25°C
From the diagram:
Photomicrograph of nail segment in KOH. Trichphyton rubrum fungal hyphae seen invading between nail cells. (dotted structure weaving through from upper left through to lower right) (DMD-108 Microscope X400)
Agar plates:
What do you need to see to diagnose an infection?
From the diagram:
Trichophyton rubrum (the more severe infectin) is a moderately slow grower, reaching maturity within 14 days at 25°C to 30°C
Back of plate- red/brown colour in the center of the plate and white at the edges
Front of plate- fluffy cloud like colonies that almost completely take over the agar
Need to see both to diagnose the infection
Treatment
- Non-prescription antifungals usually are used first Clotrimazole (Lotrimin)
- For severe athlete’s foot doctor may prescribe oral antifungal medicine (pills) eg fluconazole (Diflucan)
- Prescribed creams include butenafine (Mentax)
Candida albicans
- Part of commensal flora- digestive tract, urinary tract and/or vagina. An overgrowth leads to Candidiasis.
- The fungus grows best in warm, dark conditions and in the presence of sugar.
- Under these circumstances candida albicans changes from small dormant spores to a branching structure
- These are called a mycelium with the ability to invade and irritate tissues.
What causes Candidiasis ?
Disturbance to the normal balance of yeast and bacteria or the pH levels in the digestive or vaginal tracts can create ideal conditions for the overgrowth of yeasts
- Hormonal changes during pregnancy
- The combined oral contraceptive pill
- Steroid drugs, i.e. for asthma treatments
- Antibiotics (can cause imbalance of Lactobacillus acidophilus which leads to fungus growth)
- Diabetes - the increased levels of sugar encourage the yeasts to proliferate
Clinical presentation of candidiasis
- Heavy bloating and flatulence
- Rectal itching
- Depression and mood swings
- Muscle or joint pains Oral or vaginal thrush; cystitis
- Sore mouth and white coated tongue Red sore rash on the skin
- Cravings for sweet things
- Intolerance of alcohol
Testing for Candida Overgrowth in the laboratory
- Blood tests in which antibodies are identified: IgG (indicates an infection currently going on in the body or has just completed , IgA (indicates if infection was of mucus membranes in the body) and IgM (memory cells- recent infection that has occured) antibodies are measured
- IgM antibodies indicate a recent infection
- IgG antibodies indicate a current or past infection of Candidiasis.
- IgA antibodies can indicate an infection of the mucous membranes.
- Culture of stool samples or vaginal swabs to detect yeast overgrowth.
Laboratory results:
How are candida identified
- Candida branches out and overgrows
- prominant purple filaments
- Smell sweet
Prevention of candidiasis
Avoid all foods high in sugar and yeast
Increase immune boosting foods
Natural anti-fungal agents to help the body fight naturally against the overgrowth
Probiotics to help to re-colonise the digestive tract with beneficial bacteria
What you might see in the lab on environmental plates: Aspergillus niger
- Ubiquitous, worldwide distribution
- Found in mesophilic environments.
- One of the most common of the fungi in soil, rotting fruit & plant matter as well as many indoor environments.
- Common laboratory contaminant.
What you might see in the lab on environmental plates: Cladosporium species
- Found in soil, on plant debris and leaf surfaces.
- Generally non-pathogenic although they may be considered as possible opportunists in the severely debilitated (immunocomprimised) host
What you might see in the lab on environmental plates: Fusarium species
- Distributed in soil & associated with plants.
- Most species are harmless
- Some species produce mycotoxins in cereal crops that can affect human and animal health if they enter the food chain.
