Mycology Lecture 2 Flashcards
Most common fungal species to cause disease
Opportunistic invasive mycoses (esp. in immunocompromised patients)
Examples of opportunistic invasive mycoses
Aspergillosis, Candidiasis, Cryptococcosis, Mucormycosis, Pneumocystis
True or false: Endemic dimorphic mycoses have higher mortality rates than opportunistic invasive mycoses
False - OIM has much higher mortality rates
Normal human fungal microbiota is usually characterized as:
commensalism
Many fungi live as commensals with humans, including species such as:
Candida; Malassezia; Pneumocystis jiroveci
Candida as a normal human commensal is usually found in the ____ ___
gastrointestinal tract
Malassezia species as normal human commensals are usually found:
on the outermost layer of skin
Pneumocystis jiroceci as a normal human commensal is usually found in the _____ ___
respiratory tract
Infection (clinical sense)
fungus or immune response to fungus causes damage to host tissue
True or false: humans generally are needed for the completion of fungal life cycle
False - infections are often accidental encounters
True or false: person to person/animal to person transmission of mycoses are rare
True
What are some common themes for causing fungal diseases? (4)
- exposure
- portals of entry (damage to barriers)
- immunocompromised state of host
- fungal thermotolerance/other fungal attributes that can help them evade immune system and survive in the body
True or false: fungi grow very quickly
False - may not grow quickly
True or false: fungi may not move fast in infections
True (ex: fungal meningitis may take weeks to months to be diagnosed and to kill host)
True or false: if fungi do not grow quickly in disease, it can be hard to treat and may require life-long treatments
True
True or false: “epidemics” of mycoses are sometimes reported
True
Where do fungal infections come from?
environmental source (yeast or mold) transfers to human host through inhalation, ingestion, traumatic inoculation
Traumatic inoculation
major disruption of the skin, like through horrible wounds/bone exposed and open to the environment
Once a fungal infection has been established, it can spread through:
dissemination to other organs or via blood (hematogenous)
Portals of entry for fungal infections:
- skin
- inhalation (nasal passages, lungs, sinuses)
- mucous membranes (GI and GU tracts, eye)
- iatrogenic (catheters)
What are the three infection classification schemes?
- invasiveness (superficial, subcutaneous, or deep?)
- source of fungi (endogenous or exogenous?)
- morphology (yeast/mold/both?)
Name 6 examples of primary pathogens
- Histoplasma
- Coccidioides
- Blastomyces
- Sporothrix
- Paracoccidiodes
- Cryptococcus (which is also opportunistic!!)
Key risk factor for a primary pathogen
Exposure
Key risk factor for an opportunistic pathogen
Host and/or host response
True or false: some fungi may produce an allergenic disease
True - body recognizes fungus as an allergen; allergic bronchopulmonary aspergillosis (ABPA)
Mycotoxicosis
another fungal condition marked by specific toxin production
Aspergillus flavus produces a toxin called ____, which is found in and implicated in:
Aflatoxin; found in stored grains, corn, peanuts; implicated in liver cancer
True or false: ergotism is another fungal condition marked by toxin production and causes Saint Anthony’s Fire
True
Why have there been enormous increases in fungal infections?
- we’ve gotten better at diagnosing
2. (more importantly) large increase in at-risk population and in exposed population
Examples of increased at-risk and exposed populations for mycoses
- HIV/AIDS pandemic
- advances in medical technology (in particular, medical devices and catheters)
- climate/habitat change
- Urbanization/population growth
True or false: specific immunodeficiencies will put you at risk for specific fungal infections
True
Defects in cellular immunity (T cells) is caused by:
HIV/AIDS; solid organ transplant; medications (etc.)
Infections associated with T cell deficiencies:
most fungi, including: Candida, Pneumocystis, Cryptococcus, all endemic mycoses, (Aspergillus less common)
Defects in neutrophil number or function caused by:
chemotherapy, bone/stem cell transplants**, medications, etc.
Infections associated with defects in neutrophil number or function:
Candida, Aspergillus (common), Zygomycetes, several other molds
Methods of lab diagnosis of mycoses
histology and direct examination, culture, serology, antigen testing, PCR
Stains used for histology/direct examination
GMS “silver stain” and Periodic acid-Schiff (PAS)
other: KOH prep, Calcofluor white to stain chitin
GMS targets ____ of most fungi. GMS typically stains:
carbohydrates; black/brown on light green background
PAS stain targets _____ of most fungi. Examples include:
polysaccharides; glycogen and glycoproteins
PAS stain color
red-pink-purple
Culture usually consists of _____ ____ to prevent ____ ____
selective media; bacterial growth
Serology tests for ____ ____
antibody response (IgM or IgG specifically)
Antigen testing tests for ____ ___. Some examples include:
fungal parts (i.e. actual fungal antigens); Aspergillus galactomannan, Cryptococcal antigen, Histoplasma antigen
Direct exam pros
you can see the actual pathologic effect
Direct exam cons
- not sensitive
- difficult to identify species based on appearance alone
- can’t do susceptibility testing
Culture pros
Specific; can do susceptibility testing
Culture cons
Sensitivity; time
Antigen testing pros
generally faster
Antigen testing varies in ____ and ____
sensitivity and specificity
Antigen testing cons
No susceptibility testing
PCR pros
specific
PCR cons
- no susceptibilities
- difficult to distinguish between colonization or pathogen
Serology pros
often specific for fungus
Serology cons
- not good in immunocompromised
- may just represent colonization, not clinical disease
THM: with opportunistic infections in particular, ___ ____ are critical for treatment/cure.
host factors
THM True or false: With the best antifungal, the infection can be easily cured
False - even with the best one, may never cure an infection if the immune system hasn’t recovered
THM: ___, _____, and ___ ___ ___ contribute to risk of fungal infection
host; environment; fungus specific factors
Cutaneous and subcutaneous mycoses have __ incidence because they are ____ distributed
high; globally
Cutaneous and subcutaneous mycoses are generally __-___, and can cause ____ ____ and ____
non-fatal; significant disfigurement; morbidity
What antifungal is usually used to treat superficial/cutaneous infections?
Azoles and terbafine (affecting ergosterol synthesis)
Malassezia globosa is a _____ ____ and usually infects __ ___ in the skin
lipophilic yeast; oil glands
What diseases does Malassezia globosa cause?
- Pityriasis versicolor
2. Seborrhoeic dermatitis (including dandruff)
Malassezia globosa incidence (common or rare?)
common
Hortaea werneckii causes:
Tinea nigra
White piedra is caused by:
Trichosporon sp.
Black piedra is caused by:
Piedraia hortae
Pityriasis versicolor presents as:
patches of altered pigmentation
Why do Malassezia sp. grow in oily areas in the skin?
they can’t synthesize their own fatty acids so they use oils in our oil glands
True or false: Pityriasis versicolor may be acquired nosocomially through feeding solutions
True
Which phyla is Malassezia a part of?
Basidiomycetes
Describe Malassezia hyphae
short, slightly curved septate hyphae; extrudes conidia
What fungal species is often referred to as having a “russian doll” structure?
Malassezia
What can you use to treat Malassezia?
Topical or oral azoles
Describe the fungus that causes Tinea nigra
Ascomycete, dematiaceous mold, dimorphic, septate
What does Tinea nigra infection present as?
Painless brown or black macule on hands and feet
Tinea nigra is most common in:
Southern US
How can you treat Tinea nigra?
dandruff shampoo or topical antifungals
Piedra involves what part of the body?
the hair
True or false: White piedra and black piedra are caused by the same fungus, Trichosporon
False - only white piedra is caused by Trichosporon
Black piedra presents as:
black nodules on hair, usually scalp
True or false: Black piedra is caused by a mold with non-septate hyphae
False - hyphae are septate
Black piedra is usually found in the ____
tropics
Black piedra treatment
cutting hair, oral terbinafine
Piedra can disseminate to become _____ in ______ patients.
trichosporonosis; immunocompromised
Dermatophytes are ___ that infect _____ ___ and invade ___, ___, and ___ of the host
molds; keratinous tissue; hair, skin, and nails
What is the pathogenesis of dermatophytes?
invades the epidermis
True or false: dermatophytes often cause deep/disseminated disease in immunocompromised patients
False - rare dissemination in both healthy and immunocompromised patients
What are the three main genera of dermatophytes?
- Microsporum
- Trichophyton
- Epidermophyton
True or false: there are different groups of dermatophytes based on the natural reservoir they occupy
True (geophilic, zoophilic anthropophilic)
Geophilic dermatophytes
soil-dwellers, saprophytes, occasional pathogen
Zoophilic dermatophytes
normal host is animals, occasional human infection
Anthropophilic dermatophytes
confined to human host; person to person transmission
Tinea Capitis
infections of the hair shaft, scalp
Tinea Barbae
infections of the skin and coarse hairs of beards and mustache areas
Tinea Corporis
infections of glabrous skin (aka ringworm)
Tinea Cruris
infection of the groin area (aka jock itch)
Tinea Pedis
infection of foot, interdigital web spaces, soles (also called athlete’s foot)
Tinea Unguium
infections of nail; aka onychomycosis
How do we diagnose dermatophyte diseases?
- skin scraping (KOH)
- microscopy
- culture
- physical examination
- hair perforation test
- urease test
True or false: with Tinea corporis, there can be associated erythema due to inflammatory response
True
True or false: it is generally easy to eradicate onychomycosis through use of antifungals
False - it can often take months of oral antifungals
Trichophyton rubrum is a(n) _____ and spreads primarily via:
Ascomycete; person to person
True or false: Trichophyton rubrum forms macroconidia, but not microconidia
False: they form microconidia
Which dermatophyte forms a diffusible red pigment?
Trichophyton rubrum
Most common worldwide cause of dermatophytoses:
Trichophyton rubrum
Epidermophyton floccosum is a(n) ____ and spreads via:
Ascomycete; person to person
Epidermophyton floccosum forms what kind of conidia?
Macroconidia
Which dermatophyte forms “racquet hyphae”?
Epidermophyton floccosum
Microsporum canis is a(n) ____ and spreads via:
ascomycete; cats and dogs (zoophilic)
Microsporum canis conidia
macroconidia that are spindle-shaped and thick walled
True or false: Microsporum canis rarely forms microconidia
True
Common cause of tinea corporis
Microsporum canis
Methods of dermatophytes prevention
- avoid direct contact with fallen hair/desquamated epithelial cells
- avoid contacting fomites like combs, hairbrushes, cats, dogs, other animals
- keep high incidence areas dry
- maintain personal hygiene and disinfect shared items
Subcutaneous mycoses pathophysiology
traumatic inoculation
True or false: subcutaneous mycoses are often chronic infections that can be locally highly destructive, but usually dissemination doesn’t occur
True
Sporotrichosis is caused by _____ ____ and is found:
Sporothrix schenckii; worldwide in soil and vegetation
Sporotrichosis pathophysiology
starts as a skin ulcer, can spread to lymph nodes and spread upwards as nodules (nodular lymphangitis)
Sporotrichosis diagnosis
through culture or histology
Sporotrichosis treatment
Itraconazole, KI, Amphotericin B if severe
hyperthermia may help
True or false: chromoblastomycosis is a cutaneous fungal disease
False - subcutaneous
Chromoblastomycosis is caused by:
traumatic implantation of a dematiaceous yeast-like organism into the skin or subcutaneous tissue
True or false: chromoblastomycosis agent grows extremely quickly
False - very slowly
chromoblastomycosis presents as:
warty dermatitis, which can be ulcerated or crusted and have color to it
Epidemiology of chromoblastomycosis
tropics and subtropics, rural areas
Histology of chromoblastomycosis
brown-walled, round, non-budding fungal forms; cells with vertical and horizontal divisions, sclerotic bodies that look like copper pennies
chromoblastomycosis culture
you’d find pigmented fungi
Treatment of chromoblastomycosis primarily involves:
surgery
True or false: itraconazole or terbinafine may be used to treat chromoblastomycosis
True (but surgery is usually the easiest to eradicate fungus)
Name some examples of opportunistic pathogens
- Aspergillus
- Non-Aspergillus molds (Zygomycetes, Fusarium, Scedosporium)
- Candida
- Pneumocystis
- Cryptococcus
