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Chapter 22: Pathogenic Fungi Flashcards

1
Q

mycoses

A

among the most difficult diseases to diagnose and treat

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2
Q

Why are mycoses the most difficult to treat

A
  1. signs of mycoses are most often missed or misinterpreted
  2. fungi are often resistant to antifungal agents
  3. limited number of effective antimicrobials
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3
Q

fungi and spores

A

-are everywhere in the environment and acquired via inhalation, trauma, or ingestion
-infrequently spread from person-to-person so most mycoses are not contagious except for dermatophytes

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4
Q

dermatophytes

A

-fungi found on the skin, are the exceptions as they can be transferred via fomites
-are considered opportunistic fungi because they often occur in individuals susceptible to opportunists fungi

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5
Q

How many pathogens are true pathogens?

A

4
-they have the ability to attack and invade tissue

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6
Q

true pathogenic fungi

A

-exhibit dimorphism
-in the environment they have mycelial like growth but within the body they exist as yeast like thalli
-the yeast forms are invasive due to the production of various enzymes and proteins that facilitate infection
-mostly endemic to certain regions primarily the Americas
-can become systemic

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7
Q

opportunistic fungi

A

account for the remaining diseases

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8
Q

How are fungal groups taught ?

A

-in three categories of clinical manifestation (not taxon)
1. fungal infections
2. toxicoses
3. allergies

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9
Q

fungal infections

A

most common mycoses are caused by the presence in the body of either true pathogens or opportunists

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10
Q

toxicoses

A

acquired through ingestion
-could happen from eating poisonous mushrooms and contaminated food

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11
Q

allergies

A

most often result from the inhaled fungal spores resulting in a hypersensitivity response

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12
Q

Why is a patients history critical for diagnoses of most mycoses

A

-help identify a potential infection
-definitive diagnosis requires isolation, laboratory, culture, and morphological analysis of the fungus

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13
Q

sabourand dextrose agar (SDA)

A

-is usually used to culture fungi collected from patients
-this medium favors fungal growth over bacterial growth and you usually grow the culture at 2 temps to see both dimorphic forms
-25C = mycelia growth
- 37C = Yeast growth
-a few species may require a slightly higher temperature (30 C) to produce mycelial growth

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14
Q

What do fungi have in their membranes?

A

ergosterol which is used as a target for antifungal treatment

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15
Q

Amphotericin B

A

-the gold standard of antifungal agents but also potentially the most toxic
-most commonly used
-side effects are possible, especially in long term use
-other antifungal agents include the azole drugs, 5-fluorocytosine and griseofulvin, etc

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16
Q

Opportunistic infection treatment require two steps

A
  1. a high dose treatment to eliminate or reduce the fungal pathogens during the active infection
  2. long term maintenance therapy, sometimes lifetime, to control infection and prevent re-infection
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17
Q

The true pathogens are caused by what ?

A

-pathogenic, dimorphic fungi from the division of Ascomycota
1. histoplasma
2. Blastomyces
3. coccidioides
4. paracoccidioides (usually disseminate)
-all are acquired through inhalation
-all begin as a generalized pulmonary infection
-most cases are self resolving but they may disseminate via the blood

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18
Q

ascomycota

A

-usually asexual spores are presented in a sac like structure called an ascus with 8 1n haploid spores

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19
Q

histoplasmosis causative agent

A

histoplasma capsulatum
-mostly endemic in the southeastern united states north to Canada

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20
Q

histoplasma capsulatum

A

-most common fungal pathogen affecting humans
-mostly in the eastern US but also Africa and Asia
-the fungi is often found in moist soils containing high levels of nitrogen from bat and bird droppings
-inhalation of spores is the most common route of infection
-most cases resolve (95%) but some (-5%) progress to clinical histoplasmosis
-amphotericin B is the drug for treatment

21
Q

clinical histoplasmosis

A

-chronic pulmonary, cutaneous, systemic, or histoplasmosis

22
Q

What is the causative agent of blastomycosis ?

A

Blastomyces dermatitidis
-mostly endemic in the southeastern US north to Canada

23
Q

pulmonary blastomycosis

A

is the most common manifestation seen and is often self resolving
-initial pulmonary lesions are mostly asymptotic and symptoms when they develop are often vague respiratory symptoms
- dissemination of the fungus can occur and present cutaneously, osseously or in the CNS (in AIDS)
-treatment is with amphotericin B

24
Q

what is the causative agent of coccidioidomycosis

A

coccidioides immitis
-almost exclusively in the southwestern US

25
coccidioidomycosis
-inhalation of dust can carry arthospores, a type of asexual spores into the lung -most often results in pulmonary conditions and is often self resolving -disseminated or advanced pulmonary cases are possible then amphotericin B is the preferred drug for treatment
26
What is the causative agent of paracoccidioidomycosis
paracoccidioides brasiliensis -found in southern Mexico and South America particularly Brazil
27
paracoccidioidomycosis
-a rare disease mostly in farm workers in endemic areas -similar to blastomycosis and coccidiomycosis -infection begins as a pulmonary condition however dissemination almost always follows, unlike the 3 other -produces a chronic inflammatory disease of mucous -treatment is with amphotericin B or ketoconazole
28
What 5 genera are often encountered for opportunists?
1. Pneumocystis 2. Candida 3. Aspergillus 4. Cryptococcus 5. Mucor
29
Opportunistic mycoses
-do not typically affect healthy humans but are usually limited to people with poor immunity -they are becoming more important as the number of immunocompromised individuals rises -they can be difficult to identify because their symptoms are often atypical
30
pneumocystis jiroveci
-a very common opportunistic fungal infection of AIDS patients so it is now almost diagnostic for the patient having progressed to AIDS -infections can also result in pneumocystis pneumonia (PCP) as it colonizes the lungs and if left untreated progressively damages the lungs resulting in death -due to organisms similarities to protozoa it was formerly classified as a protozoan, treatment is with anti-protozoan drugs like trimethoprim or sulfanilamide
31
candida albicans
a common member of the microbiota of the skin and mucous membranes is the most common causative agent of this genus -is one of the few fungi that can be transmitted between individuals so it is contagious -all cases of the disease are from opportunistic infection -treatment depends on infection site (oral and/ or topical)
32
What infections can candida albicans cause
1. thrush 2, diaper rash 3. onychomycosis 4. ocular candidiasis 5. vulvovaginal yeast infection
33
aspergillosis
-caused by fungal species in the genus aspergillus -it can be found throughout the environment and pulmonary disease occurs from the inhalation of the fungal spores -non-pulmonary diseases including cutaneous and systemic aspergillosis can also result -treatment can include allergy medicine for hypersensitivity reactions (allergies) or amphotericin B along with other antifungals for others diseases (sinusitis, external otitis, etc)
34
What is the causative agent of cryptococcosis
-cryptococcus neoformans -infections can result in the inhalation of airborne spores found in bird droppings
35
What diseases result from cryptococccis?
-primary pulmonary cryptococcus (asymptomatic or mild pneumonia) -cryptococcal meningitis (most common clinical form of infection, follows dissemination of the fungus to the CNS) -treatment is synergistic combination of amphotericin B and 5-fluorcytosine
36
zygomycoses
-infections caused by fungi in the division Zygomycota, usually by the genus Mucor -most commonly seen in individuals with uncontrolled diabetes, people who inject illegal drugs, in some cancer patients, an in some patients receiving antimicrobial drugs as a secondary infection -
37
What diseases come from zygomycoses
-dissemination can occur and result in various conditions 1.Rhinocerebral zygomycosis (nose--> brain) 2. Pulmonary zygomycosis 3. gastrointestinal zygomycosis 4. cutaneous zygomycosis -treatment is with IV amphotericin B for 8-10 weeks
38
Fungal opportunists in immunosuppressed individuals
-AIDS patients have permanent immune dysfunction making a full cure of opportunistic infections unlikely -mycoses accounts for most deaths associated with AIDS therefore they are great concern -pneumocystis jiroveci, candida albicans, aspergillus fumigatus, and cryptococcus neoformans are so common in HIV positive individuals their mycoses partly defined end stage AIDS
39
What are some emerging fungal diseases?
-problematic because of increasing number of immunosuppressant people 1. fusarium 2. penicillium marneffei 3. trichosporon beigelii
40
fusarium
species causes respiratory distress disseminated infections, and fungemia
41
penicillium marneffei
causes pulmonary diseases upon inhalation
42
trichosporon beigelli
cause a disseminated and drug resistant infection in AIDS patients often fatal -can also cause white Piedra (disease of the scalp) which is not associated with AIDS and treated by shaving the area and applying terbinafine
43
superficial , cutaneous and subcutaneous mycoses
-the most commonly reported fungal diseases -all are opportunistic and can be transferred via environment exposure or more common by direct contact -dermatophyte mycoses are usually localized at or near the surface -can be acquired by healthy individuals via person-to-person contact or through environmental exposure -diseases are usually not life threatening but they can be chronic or recurring nuisance infections
44
dermatophytoses
-fungal infections of the skin or nails are caused by dermatophytes which feed on keratin of dead tissue -they do not comfortably fall into opportunist or true pathogens categories so we discuss them separately -they were previously called ring worms -treatment is with topical antifungal agents (terbinafine) -common infections: tinea pedis (worm of the foot) more commonly called athletes foot tinea cruris (in the groin( called jock itch tinea corporis (ringworm) of the body
45
What are the 2 genera of ascomycetes caused most by dermatophytoses
1. Trichophyton 2. Microsporum 3. Epidermophyton fluccosum
46
mycotoxins
caused by eating foods contaminated with fungal toxins
47
mycetismus
mushroom poisoning from wild mushroom
48
ergot alkaloids
are used to make 1. illegal and dangerous recreational drugs (lysergic acids) (LSD) 2. prescription drugs for migraines (ergotamine) or labor induction (ergometrine) -some fungal allergens can elicit a hyper sensitive response in sensitivity -from inhalation, ingestion, or other contact
49
mycetismus
-most mushrooms are not toxic but only people with experience in mycology should pick their own wild mushrooms for consumption from the environment -mushrooms that produce poisons/toxins can cause neurological dysfunction, hallucinations, severe organ damage or death -recreational intake of psilocybe (magic mushroom) falls into this category -poisoning typically occurs when untrained individuals or young children pick and eat wild mushrooms -the deadliest mushroom toxin is produced by death cap mushroom amanita phalloides

Microbiology (13 decks)

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