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Microbiology > Chapter 22: Pathogenic Fungi > Flashcards

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
Q

coccidioidomycosis

A

-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
Q

What is the causative agent of paracoccidioidomycosis

A

paracoccidioides brasiliensis
-found in southern Mexico and South America particularly Brazil

27
Q

paracoccidioidomycosis

A

-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
Q

What 5 genera are often encountered for opportunists?

A
  1. Pneumocystis
  2. Candida
  3. Aspergillus
  4. Cryptococcus
  5. Mucor
29
Q

Opportunistic mycoses

A

-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
Q

pneumocystis jiroveci

A

-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
Q

candida albicans

A

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
Q

What infections can candida albicans cause

A
  1. thrush
    2, diaper rash
  2. onychomycosis
  3. ocular candidiasis
  4. vulvovaginal yeast infection
33
Q

aspergillosis

A

-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
Q

What is the causative agent of cryptococcosis

A

-cryptococcus neoformans
-infections can result in the inhalation of airborne spores found in bird droppings

35
Q

What diseases result from cryptococccis?

A

-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
Q

zygomycoses

A

-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
Q

What diseases come from zygomycoses

A

-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
Q

Fungal opportunists in immunosuppressed individuals

A

-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
Q

What are some emerging fungal diseases?

A

-problematic because of increasing number of immunosuppressant people
1. fusarium
2. penicillium marneffei
3. trichosporon beigelii

40
Q

fusarium

A

species causes respiratory distress disseminated infections, and fungemia

41
Q

penicillium marneffei

A

causes pulmonary diseases upon inhalation

42
Q

trichosporon beigelli

A

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
Q

superficial , cutaneous and subcutaneous mycoses

A

-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
Q

dermatophytoses

A

-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
Q

What are the 2 genera of ascomycetes caused most by dermatophytoses

A
  1. Trichophyton
  2. Microsporum
  3. Epidermophyton fluccosum
46
Q

mycotoxins

A

caused by eating foods contaminated with fungal toxins

47
Q

mycetismus

A

mushroom poisoning from wild mushroom

48
Q

ergot alkaloids

A

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
Q

mycetismus

A

-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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