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What is the essential sterol in fungi?
What class are fungi?
- most are strict aerobes
- NO strict anaerobes
Describe a Fungal cell
- •They possess at least one nucleus
- surrounded by a nuclear membrane
•Have cytoplasmic organelles
•Cell membrane contains sterols (ergosterol*)
What DONT fungal cell walls have?
- muramic acid
- teichoic acids
What DO fungal cell walls possess?
- Hexos and hexosamine polymers
What is chitin?
composed of gluocosamine subunits (linked like cellulose)
Describe the Fungal cell memebrane
- –Contains phosphatidylethanolamine
- (phospholipid) and phosphatidylcoline
- –Ergosterol and zymosterol – major sterols
- –Cholesterol is usually absent
- Functions as an osmotic barrier.
- Facilitates synthesis of cell wall material
Heterophilic metabolism: what do fungi require as an energy source?
Where di saprophytis derive nutrients from?
decaying oraganic material-- will grow on simple carbon source nitrate ions as a nitrogen source
How does heterophilic metabolism occur?
- - absorptive mode of nutrition - secrete digesting enzymes into environment - simpler
- substances from digested macromolecules enter cell by osmosis or specialized transport systems
What is the morphology of yeast?
- smooth colonies like bacteria; microscopically - single cells which bud
- fuzzy colonies microscopically how the cell to extend by formation of tube-like extensions with thinck parallel walls called HYPEA
- Separate or non separate
- A mass of hypea= mycelium
What does dimorphism mean? in regards to fungi?
- Fungi can grow as yeast or mold
- Some fungi can grow as either phase
What does dimorphism depend on?
What is the difference between mold and yeast in regards to their location/temperature?
- Yeast-- usually found WITHIN a system so can live inside a body
- Mold form-- room temperature
This is CANDIDA ALBICANS:
Name some features
- Dimorphic fungi
- grow as budding yeast cells
- filamentous hyphae (bottom of picture)
- intermediate forms
- *most important fungi
Do most Fungi have a sexual spore phase?
How is a sexual spore produced?
fusion of 2 nuclei that general undergo mitosis
Is sexual mating necessary for continuation of the fungal species?
- asexual spores continus to maintain and disseminate these species
- = reproductive elements producers by:
- -budding off of conidiogenous hypae
- - differentiation of preformed hypae
- = reproductive elements produced by:
- -consecutive cleavages of a sporangium
- -major method for maintenance and dissemination of many fungi*
formation of a bud in yeasts
produce separate or non separate hyphae which extend to from a mycelium
- branching tubular structures that make up the mycelium
- septae divide the hyphae into compartments (not cells)
Conencocytic hyphae (non-septate)
- considered more primitive.
- when hyphal strand is damaged, entires strand dies!
- pores between adjacent compartments can be plugged preventing death of entire strand
based on sexual spores and septation
- gametes and asexual reproduction with the formation of zygospores
- Asexaul spore: Sporangiospore
- ascus with the production of ascospores
- Asexaul spore: Conidia
- basidium with the production of basidospores
- Asexaul spore: Conidia
- no recognizable form of sexual reproduction
- Asexaul spore: Conidia
- -Histoplasma capsulatum
- Superficial skin fungi
- indolent lesions of the skin and its appendages
- Ex: ring worm, athlete's feet
What are the most virulent fungi?
- systematic pathogens
- can caused serious progressive disease in previously healthy people
Pathenogensis of fungi
- most are oppurtunistic
- 1000/s of aerosol conidia and spores inhaled daily
- some are normal flora
- systematic infections= uncommon
- progressive systematic fungi infections= most difficult to diagnosis and therapeutic problems in infectious disease (esp in immunocompromised)
- spores/components= could be allergen. sting hypersensitivity rxn does not require growth or viability of the fungus
- extracellular enzymes
- phagocytic interactions
- tissue injury
adherence of fungi
- Some yeasts can colonize mucosa of GI/UG
- require surface adhesion on the microbe and a receipt on the epi cell
invasion of fungi
- across surface barrier.
- may be though mechanical breaks in epithelium
Ex of invasion of fungi
C. albicans-- form hyphae and pseudohyphae that allow penetration and spread (mechanism unknown)
Phagocytic interactions of fungi
- neutrophils and macrophages are able to kill hyphae of most fungi
-dimorphic species are more resistant to killing by neutrophils
Ex: of dimorphic fungi which are yeasts at one temp and transform to hype at another temp
- C. albicans
- yeast @ 25d C
- hyphae @ 37d C
- contanins component in the call of its conidial (infective phase that is antiphagocytic
- hyphae convert to a spherule phase in tissue and become resistant
Tissue injury by fungi
- - none of the extracellular products of
- opportunistic fungi have been shown to injure the host directly
- - exotoxins / mycotoxins are produced in the environment by a number of fungi but not in
- - injury caused by fungal infections is due to
- the inflammatory and immune responses
- stimulated by the prolonged presence of the fungus.
Immunity of fungi
- intact immune response prevents infection by fungi and progressive disease
- T-cell mediated response of Primary importance
- progressive fungal diseases occur in immunocompromised patients
HUmoral immunity of fungi
-opsonizing antibody effective in some yeast infections
Ex: of humoral immunity of fungi
- Cryptococcus neoformans -antibody controls infection
- enhances killing by phagocytes
- capsule of C. neoformans antiphagocytic - antibody to capsule similar to encapsulated bacterial pathogens
Cellular immunity fo fungi
- systematic disease associated with deficiencies in neutrophils and T-cell mediated immunity
- fungi that escapee neutrophils grow slowly in macrophages
Cultivation of Fungi: physiological considerations
- O2: (most= aerobic)
- temp : mesophilic
- Moisture: 75-95% humidity
- pH tolerance: 5-6 optimal
- Generation time: yeasts= 2-3 days. molds= 1-3 WKS
Sabouraud Dextrose Agar
◦ traditional growth media for fungi
◦ peptone, dextrose at pH 5.6
◦low pH retards growth of many bacteria
- ◦NOT the best medium because it SUPPRESSES
- conidiation and PROMOTES MYCELIAL GROWTH
Why is SDA not the best growth medium for fungi?
SUPPRESSES conidiation PROMOTES MYCELIAL GROWTH
Isolate fungi from clinical specimens? Use what agar?
SDA with chloramphenicol
Mycosel (Mycobiotic) agar
◦ isolate clinical fungal specimens
- ◦ same as SDA but with chlormephenicol actidione
◦ @ pH 6.8
Dermatophyte Test Medium (DTM)**
◦ used to isolate dermatophytes from clinical skin and nail specimens
- ◦ contains cycloheximdes, gentamycin, and
- chlortetracycline to suppress common bacteria and non-fermatophilic fungi
Brain Heart Infusion agar
- nutrient enriched
- primary to grow yeast cultures especially with dimorphic fungi
Potato Dextrose Agar
deficient medium used to stimulate sporulation of many fungi
Corn Meal Agar
most commonly used to induce condition of fungi that do not produce sufficient spores on SDA, DTM, or Mycosel
- Mold ID
- microscopic characteristic of fungi
- direct microscopic examination of skin scrapings
- Mold ID
- lactophenol cotton blue
- miscroscopic examination of cultures
ID by sugar fermentation, sugar assimilation and some biochemical patterns
- Direct examination of pus, fluid, or tissues
- 10 – 20% KOH
- Heat slide and observe under microscope
- Use 20X or 40X magnification
- Fungi remain intact while tissue cells are disrupted
- Culture - use media containing antibacterial antibiotics
KOH is useful to see...?
What does a PAS tell you?
stain all fungi and are very helpful for detection of fungi in tissue sections
Fungi Elicit 3 Types of Conditions in Humans
- 1. Allergy - IgE - mold allergy Non-complicated Type I
- 2. Toxins - Aflatoxins
- 3. Disease - mycosis