Fungi Flashcards
Compare and contrast the ribosomes and cell wall make-up of bacteria and fungi
- Bacteria are prokaryotes while Fungi are eukaryotic heterotrophs
- Bacteria have peptidoglycan cell wall while fungi have cell wall made of b-glucan and cell membrane made of ergosterol
- Fungi have 80s ribosomes while bacteria have 70s ribosomes
Since fungi are more similar to animal cells than are bacteria, anti-fungal treatments are
harder to develop (fewer molecular targets) and will most likely have greater toxicity
Two main types of fungi are
1) yeast = single-celled, reproduce by budding
2) molds = grow in hyphae/mycelia and have complex reproduction
Both yeast and molds make new cells by fungal mitosis
Both yeast and molds make new cells by fungal mitosis. Yeast in particular (and some others) have closed mitosis. What is closed mitosis?
Closed mitosis is when the nuclear envelope does not disperse.
Some molds can undergo asexual reproduction and produce asexual spores (conidia). List the 5 asexual spores and why are they useful?
- Arthrospores
- Chlamydospores
- blastospores
- condidospores
- sporangiospores
They have distinct characteristics which can be seen under microscope and help diagnose the particular fungal infection
What is thermal dimorphism?
When certain fungal pathogens will grow as molds in the environment at 24C and as yeast in the human body (37C)
Which form (mold vs yeast) has more immune-evasive properties?
Yeast form
Why can dual cultures be useful in fungal infection?
Dual cultures in different temperatures are helpful in determining if there’s thermal dimorphism.
Describe the immune response to fungal infection
1) form granulomas mediated by macrophages and T helper cells
2) sometimes also pus-forming (suppurative)
Explain how someone can confuse a fungal infection for TB
Because both form granulomas
Most fungal pathogens are environmental except
Candida albicans which is part of normal flora/opportunistic pathogen.
Fungi can grow in what types of environment that bacteria cannot
more acidic, drier, colder, and higher-osmotic pressure environments.
The ability of fungi to grow in a certain type of environment enables them to cause what types of infections and do what to food?
more cutaneous infections and spoilage of food
T/F: Most fungal pathogens have little contagion or drug resistance
True
T/F: Fungal pathogens can be eradicated
False; there is currently no eradication
What causes mycotoxicosis? Is mycotoxicosis a form of fungal infection?
eating fungal toxins (wrong mushrooms, spoiled food); it is not a fungal infection
People can have fungal allergies, which can be very dangerous
True, some people can develop an asthmatic reaction to certain fungi.
Can you use PPD to diagnose certain fungal infections?
Yes
KOH-mount microscopy can be used to diagnose fungal infections. Explain the purpose of the KOH
10% KOH is added to the tissue sample to break down the tissue while preserving the fungi for examination under the microscope
What do you culture fungi on?
Sabouraud’s agar
Besides microscopy and culture, what else can be used to diagnose fungal infections?
DNA probe and PCR, serology
For dangerous systemic fungal infection, one can perform what test?
PCR
To study the epidemiology of a fungal infection, one can perform what test?
serology
What are the 3 major classes of anti-fungal drugs and what do they do?
1) Polyenes (i.e. amphotericin B) -disrupt fungal cell membranes at ergosterol insertion sites
2) Azoles (inhibit ergosterol synthesis)
3) Echinocandins (inhibit beta-glucan synthesis)
Which anti-fungal is highly effective and broad-spectrum and can even be used in pregnant women with systemic fungal infections?
Amphotericin B, but nephrotoxic
Azoles are less toxic. Which is the major drug in this class and what does it treat?
Fluconazole/Diflucan treats candidiasis and cryptococcosis
Echinocandins are also low toxicity. This class is highly effective against which 2 fungal infections?
1) candida
2) aspergillus
List whether or not if gram stain can be performed on culture of fungus, virus and/or bacteria
Gram stain can be done on culture of bacteria and on culture of fungus if the fungus is candida
List whether or not if examination by light microscope can be performed on culture of fungus, virus and/or bacteria
Light microscope can examine culture of bacteria and culture of fungi. In the case of the culture of virus, the light microscope will be looking for cytopathic effect.
List whether or not if macroscopic apperance of colony morphology can be performed on culture of fungus, virus and/or bacteria
Macroscopic appearance of colony morphology can be used on fungi culture and on bacterial culture (unless the bacteria is intracellular)
List whether or not if DNA probes/PCR can be performed on culture of fungus, virus and/or bacteria
DNA probes/PCR can be used on all three cultures. In the case of RNA viruses, make sure it’s RT-PCR.
List the 4 subtypes of fungal infection and provide an example for each
1) superficial mycosis -dermatophytosis
2) subcutaneous mycosis -sporotrichosis
3) systemic mycosis -coccidiomycosis
4) opportunistic mycosis -cryptococcosis
Does superficial mycosis require thermal dimorphism?
No
Dermatophytes causing fungal growth on superficial skin layer (superficial mycoses) infect only
superficial keratinized structures (hair, skin, nails)
Dermatophytes produce what that allow invasion of cornified cell layer
keratinase
Is dermatophytosis very common?
Yes, it is very common and caused by three different genera of fungi
What are some of the minor symptoms that dermatophytosis (a superficial mycosis) cause?
1) tinea cruris (jock itch)
2) tinea pedis (athlete’s foot)
3) tinea corporus (ringworm)
Why is it important to treat all affected body sites of a patient with superficial mycosis (i.e. dermatophytosis) simultaneously with topical antifungal cream/azoles?
Because one route of transmission is autoinnoculation when the patient’s affected body part infects another part of the patient. It can also be transmitted by fomites.
If topical antifungal cream fails to treat all affected body parts of a patient with dermatophytosis (superficial mycosis), is there an alternative treatment?
give oral griseofulvin
How does one get a subcutaneous mycosis?
It is introduced by trauma (puncture wound), exposing subcutaneous tissue to soil or vegetation.
Generally, is there a slow or fast spread from trauma site toward trunk by lymphatics in patients with subcutaneous mycosis?
There is a slow spread from trauma site toward trunk by lymphatics.
Patients with subcutaneous mycoses may present with what type of history with antibiotics?
Patients will have history of ineffective antibiotic treatment
How to diagnose superficial mycoses?
KOH mount, culture
How does one treat someone with subcutaneous mycoses? Does treatment differ if it’s a serious case vs mild case?
Normally, treat patients with oral azoles, but in serious cases, give patients amphotericin B and maybe perform local surgery.
Does subcutaneous mycosis require thermal dimorphism?
Yes, need to be in yeast form to spread.
Sporotrichosis, an example of subcutaneous mycosis, is caused by which organism? Explain this organism’s route of entry into body.
sporothrix spp is a thermally dimorphic fungi of vegetation that enters skin thru small injuries (thorns, splinters)
In sporotrichosis, the yeasts grow at site and form
painless pustule or ulcer that spreads up lymphatics over years
Patients infected with sporotrichosis have symptoms that wax and wane over the years. But if the patient is immunosuppressed, then what kind of symptoms will you expect?
disseminated disease and meningitis
Patients infected with sporotrichosis have symptoms that wax and wane over the years. But if the patient has COPD and/or is on long-term corticosteroid use, then what kind of symptoms will you expect?
pulmonary symptoms that are hard to distinguish from TB or histoplasmosis
What’s the best way to diagnose sporotrichosis (a subcutaneous mycosis)?
culture at room temperature on sabouraud’s agar from pus. But can also do tissue biospy
How do you treat someone with sporotrichosis? WHat if the case is serious?
Treat with oral azoles, but if serious, treat with amphotericin B
List themes of Systemic mycoses
- environmental: spores/fungi in soil
- inhaled into lungs
- thermal dimorphism
- wide range of severity depending on dose of infectious org and host’s immune status
- NOT person-to-person transmissible
Systemic mycoses can mimic TB. What is a way to differentiate the two?
Source of systemic mycoses is most likely in American soil, not foreign crowds in the case of TB.
Coccidioidomycosis is an example of a systemic mycosis caused by the organism coccidiodes. It is endemic to
US Southwest
Coccidiodes is thermally dimorphic. Explain
- mold grows in wet weather
- mold releases arthrospores (asexual spores) in dry
- spores are inhaled into lungs
- in lungs, the temperature increase will allow conversion to spherules.
- spherules erupt to make endosomes
- endosomes make more spherules
T/F: Outcomes of Coccidiodomycosis (a systemic mycosis) are dependent on infectious dose and patient’s immune status.
True
What is the outcome of a patient with Low dose of coccidiodes, healthy innate system?
asymptomatic clearance.
T/F: About 30% of people with coccidiodomycosis (a systemic mycosis) will asymptomatically clear the infection.
False, it is about 60% of the cases
What are the 3 possible outcomes of a patient with moderate dose of coccidiodes, healthy CMI (form granulomas)?
1) asymptomatic clearance
2) non-specific flu-like symptoms
3) mild pneumonia
What are the outcomes of a patient has a high dose of coccidiodes and/or immunosuppressed?
1) serious pneumonia
2) dangerous dissemination
A moderate dose of coccidoides can cause Valley fever aka desert rheumatism. What are the symptoms?
1) fever
2) erythema nodosum
3) erythema multifrome
4) arthralgias
5) chest pain
Risk factors of coccidiodomycosis:
age (older) race (filipinos and blacks) pregnancy immunocompromised occupational high exposure.
Ways to diagnose coccidiomycosis (a systemic mycosis)?
exam, history, PPD, biopsy for spherules, culture, serology for dissemination
Patients with coccidomycosis who are predisposed to complications should receive what drug?
oral azoles
Patients with coccidomycosis who present with meningitis should receive what drug?
fluconazole
Patients with coccidomycosis who are either pregnant or have disseminated disease should receive what drug?
amphotericin B
What is the optimal treatment for someone with opportunistic mycosis?
Opportunistic mycosis occurs depending on patient’s pre-existing conditions. Hence, it is impt to treat both the infection and the underlying cause. (Ex. Is the patient’s diabetes contributing to the manifestation of fungal infection?)
Cryptococcis is an example of an opportunistic mycosis. There are 2 different species. Which one did we focus on in class?
c. neoformans (environmental, found worldwide, characteristic oval yeasts with narrow based buds and wide polysaccharide capsule)
Under microscopy, you see spherules, which are diagnostic of which type of fungal infection?
systemic mycosis, specially coccidiodomycosis.
Under microscopy, you see characteristic oval yeasts with narrow based buds and wide polysaccharide capsule, which are diagnostic of which type of fungal infection?
opportunistic mycosis, cryptococcus
Cryptococcus will suppress host inflammatory response (low inflammation). In the later stages, patients will get cryptococcal meningitis. What are three reasons why there’s been a spike in such cases?
- use of steroids
- survival with malignancy
- AIDS
Routine blood work may be normal for someone infected with cryptococcosis. What are some other ways to diagnose the infection?
CSF
Biospy
microscope (“crag”)
How to treat someone with cryptococcosis?
combinations of azoles and amphotericin B
