Fungi Flashcards
Three Reasons Why Fungi Are Hard to Classify
- Fungal cell wall is very thick, PCR takes a long time
- There is no “system” for identifying them, so it is all pattern recognition. Tech takes a slide, puts it under a microscope, and looks for patterns
- Eukaryotes grow slower. Test results can take up to SIX WEEKS for MOLDS or 72 HOURS for YEAST for it to grow sufficiently for identification
Classification of Fungal Infections
They are classified based on where they occur
- Superficial/Cutaneous Mycoses
- Skin and nails, primarily dermatophytes
- BREAK DOWN KERATIN - Subcutaneous Mycoses
- Embedded (AND THATS LITERALLY ALL HE SAID) - Systemic Mycoses
- In the blood - Opportunistic Mycoses
- Affecting the immunocompromised
Common Targets of Antifungal Therapies
Often target the chitin component of the outer cell wall
OR
Target ergosterol within the outer cell wall membrane. Recall the structural similarities with cholesterol and the side effects produced
Compare and Contrast Bacteria and Fungi
- Bacteria are single-celled and prokaryotic
- Fungi are multicellular (molds) and eukaryotic
- Bacteria tend to be toxic by their SECONDARY PRODUCTS
- The cellular overlap between eukaryotic human cells and eukaryotic fungi makes them more inherently toxic
- Fungi are more difficult to treat due to their higher INTRINSIC RESISTANCE
- Bacteria are very simple on a cellular level, whereas yeasts are quite complex as eukaryotes
- Yeasts do not cause pneumonia, whereas bacteria do
Exceptions to the Yeast/Mold Distinction
Some fungi are yeasts and one temperature and molds at another
Four Uses of the Fungal Cell Wall
- Fungal cell wall contains ergosterol
- Gives shape to the fungi
- Gives strength to the fungi by protecting from solvents and UV light
- Secretes enzymes from the cell walls which allows them to hydrolyze sugars
Fungal Cell Wall Components
MOST ANTIFUNGALS TARGET THE CELL WALL
OUTER LAYER
- Used for communication, budding, and replication
Three layers:
Beta-glucans
CHITIN (major structure)
Cell membrane
Fungal Cell Wall Features
- No peptidoglycan
- Major structure is chitin
- Exploited for diagnosis
- New drugs target the cell wall
Fungal Reproduction
- Primary reproductive structure
Primary Reproductive structures: SPORES or CONIDIA
Spores disseminate, transfer, and transmit fungi
Key Target of Anti-Fungal (Yeast) Therapies, and its side effects in humans
Our cells use cholesterol to maintain membrane fluidity, and for communication
Fungi use ERGOSTEROL, which is structurally quite similar to cholesterol. This is the TARGET for many antifungal therapies as it is a KEY COMPONENT of the yeast CELL WALL
- The structural similarity to cholesterol produces many side effects in humans
Laboratory Detection of Fungi
- Technique
- How long it takes
- Gram stain, observe with microscopy
- May see fungal elements but microscopes are not highly sensitive so you can’t rule it out
- Cultured on special media
Time
Yeast: 1-3 days
Dermatophytes: 1-3 weeks, but up to six weeks
Systemic fungi: 3-6 weeks
Opportunistic Mycoces
- Definition
- Most common one
Definition
- Fungi considered ‘non pathogenic’ but can cause significant illness in the immunocompromised, those with prosthetic/intravascular devices, and hematologic malignancies
Most common: Aspergillus molds
- Invasive aspergillosis has become the major cause of morbidity and mortality in immunocompromised patients, with mortality rates as high as 88%
Opportunistic Mycoses
- Common cause of infection
- High risk populations
Infection by aspergillus, which is found in the environment, occurs via inhalation of spores that eventually can cause pneumonia
- Almost 2/3rds of PTs with invasive aspergillosis have
- an underlying hematologic disease
- or have undergone bone marrow transplants
Opportunistic Mycoses
- Common clinical presentation
Opportunistic infections by molds can often result in
- Sinus infection
- Respiratory disease
- Fungemia
Things to know for quiz
Dimorphics
Systemics (aspergillus, cryptococcus)
Yeasts
Know what a dermatophyte is and what it infects
Two Broad Groups of Fungi and their Distinction
Yeast
- UNICELLULAR
Mold
- MULTICELLULAR
Yeast - Cellular Components
- Cell wall
- Endoplasmic reticulum
- mitochondria
- membrane bound nucleus
Yeast vs Mold
- Reproduction and consequences
Molds reproduce sexually, much slower
Yeasts reproduce by budding (binary fission), much faster
