Mycology II Flashcards
What is the form of nutrition of most fungi?
saprophytic or parasitic to plants
Do fungi infect humans and animals?
chance event, only occuring when conditions are favorable.
Most fungi are what type of pathogens? What is the exception?
opportunistic pathogens!
exception: primary pathogens causing systemic mycoses and dermatophytes –> dimorphic fungi
What yeastst have adapted to human and animal environments?
Candida and Malassezia
What determines if a fungal infection will cause a disease?
the complex interplay between fungal virulence factors and host defense factors
What does infection depend on?
- inoculum size
- the general immunity of the host.
What are the virulence factors allowing for fungal pathogenicity?
- Ability to adhere to host cells by way of cell wall glycoproteins.
- Production capsules allowing them to resist phagocytosis.
- Ability to acquire iron from red blood cells as in Candida albicans.
- Ability to damage host by secreting enzymes such as keratinase, elastase, collagenase.
- Ability to resist killing by phagocytes as in dimorphic fungi.
- Ability to secrete mycotoxins.
What are teh two forms of host defence factors?
1) Physical barriers, such as skin and mucus membranes
2) Chemical barriers, such as secretions, serum factors
State examples of host defence factors.
Physical barriers = SKIN & MUCOUS MEMBRANES
The fatty acid content of the skin
The pH of the skin, mucosal surfaces and body fluids
Epithelial cell turnover
Normal flora
Chemical barriers = SECRETIONS AND SERUM FACTORS
Most fungi are mesophilic and cannot grow at + 37 C.
At what temperature is it difficult for fungi to grow at?
37C+
What is the professional name used to describe a fungal disease?
mycoses
Many fungal infections of the skin involve what type of fungi?
fungi that are found in the normal skin microbiota.
When can fungi that are found in the normal skin microbiota cause an infection?
when they gain entry through a wound
How do fungi usually cause opportunistic infections?
in immunocompromised patients
What type of environments promote fungal growth?
moist
What are mycoses?
fungal infections
How are mycoses classified?
based on their invasiveness:
- cutaneous mycoses
- subcutaneous mycoses
- systemic mycoses
What are cutaneous mycoses?
Mycoses that cause superficial infections of the epidermis, hair, and nails.
What are subcutaneous mycoses?
Mycoses that penetrate the epidermis and the dermis to infect deeper tissues.
What are systematic mycoses?
Mycoses that spread throughout the body.
What are cutaneous mycoses called tineas caused by?
dermatophytes (that require keratin, a protein found in skin, hair, and nails, for growth.)
What are the three genera of dermatophytes which cause cutaneous mycoses?
Trichophyton,
Epidermophyton,
Microsporum.
What is the favorable environments of dermatophytes?
- moist
- dark
What causes aspergillosis? What is it?
A fungal disease caused by molds of the genus Aspergillus.
- primary: less common: begins in skin
- secondary: more common: beings in the respiratory system
- result: distinctive eschars that form at the site or sites of infection
- COMMON HOSPITAL AQUIRED INFECTION
What do yeasts of the genus Candida cause?
opportunistic infections of the skin called candidiasis, producing intertrigo, localized rashes, or yellowing of the nails.
What are the infections called when they are caused by fungi which invade immunosupressed hosts?
opportunistic infections
What diseases are marked by respiratory distress?
Cryptococcosis(Cryptococcus), Histoplasmosis (Histoplasma)
What yeasts cause skin infections referred to as cutaneous candidiasis?
Candida albicans and other yeasts in the genus Candida.
What is ‘intertrigo”?
A general term for a rash that occurs in a skin fold, or other localized rashes on the skin.
How is Candidiasis of the skin and nails is diagnosed?
- clinical observation
- culture,
- Gram stain,
- KOH wet mounts.
- susceptibility testing for anti-fungal agents
What type of mycoses can spreak from the skin to deeper tissues?
cutaneous mycoses are superficial, subcutaneous mycoses.
In temperate regions, what is the most common subcutaneous mycosis? What is it caused by? How can it be avoided?
sporotrichosis, –> fungus Sporothrix schenkii
- commonly known as rose gardener’s disease or rose thorn disease.
- ontracted after working with soil, plants, or timber, as the fungus can gain entry through a small wound such as a thorn-prick or splinter.
- avoided by wearing gloves and protective clothing while gardening and promptly cleaning and disinfecting any wounds sustained during outdoor activities.
What is a ringworm?
Ringworm is an infection of skin, hair, or claws caused by a type of fungus.
How is ringworm spread?
Most cases of ringworm are spread by contact with infected animal or contaminated objects such as furniture or grooming tools.
Does contact always result in infection?
no!
Where do dermatophytes grow? Where does the infection stop?
- grow only in the dead cells of skin and hair
- infection stops on reaching living cells or inflamed tissue
Can dermatophytes colonize the cornified structures (hair, claws) and the stratum corneum and cause disease without ever entering living tissue?
yes!
Whet are the most contageous fungal infections caused by?
dermatophytes
What environments do dermatophytes favour?
hot and humid
What animals are more succeptible to dermatophyte infection?
- animals kept in overcrowded, dirty, or damp areas,
- animals with inadequate nutrition,
- immunosuppressed animals.
What is the principal way of resolving an infection?
cell-mediated immune response.
Dermatophytosis is caused by fungi in what genera?
Microsporum, Trichophyton and Epidermophyton.
What type of pathogens (animal or human) are dermatophytes?
Microsporum, Trichophyton = Animal pathogens
Epidermophyton = Human pathogen
How are dermatophytes classified?
- Zoophilic
- Anthropophilic
- Geophilic
Where are zoophilic dermatophytes mainly found?
in animals but can be transmitted to
humans.
Where are anthropophilic dermatophytes mainly found?
in humans and are very seldom (rarely) transmitted to animals.
Where are geophilic dermatophytes mainly found?
in soil, where they are associated with
decomposing hair, feathers, hooves and other.
- infect both humans and animals
What does ‘endothrix’ refer to?
dermatophyte infections of the hair that invade the hair shaft and internalize into the hair cell.
What does ‘exothrix (ectothrix)’ refer to?
A dermatophyte infection which remains confined to the hair surface.
What is the shape of Trichophyton and Microsporum
Trichophyton- cylinder
Microsporum- spindle
What is the main reservois for microsporum canis? Can it be transmitted to humans? How?
- cats and dogs
- can also be transmitted to humans through direct and indirect contact with animals
and fomites such as combs, brushes, hats, furniture, linens etc. - Microsporum canis can infect all mammals.
How does Microsporum canis reproduce?
two conidial forms,
1) large, spindle-shaped, multicell macroconidia
2) small, single celled microconidia.
What does microsporum canis produce?
- septate hyphae,
- macroconidia,
- microconidia.
On what media does Microsporum canis grow?
Sabouraud dextrose agar
- +25°C
- 7 days
- no specific growth factor or nutrition requirements (grows well on most commercially available media)
What is the shape of Microsporum canis?
Macroconidia:
- spindle-shaped,
- asymmetrical apical knob.
- 6- to 15-celled, long,
- rough
- thick outer cell walls.
- thin septal walls
Microconidia:
- rare,
- unicellular
- clavate/pyriform
What animals are susceptible to dermatophytes?
all domestic animals!
* Dogs and cats
* Cattle
* Sheep and goats
* Horses
* Swine
* Rodents, rabbits
* Birds
What is the incubation period of dermatophytes?
7 days to 4 weeks (cultivation at room temperature)
Where do dermatophytes only grow in humans?
only in keratinized tissues
What are the clinical signs of dermatophytes?
Alopecia
Scaling, crusts
Erythema, pruritus
“Ringworm” appearance uncommon
State the main fungus genera and species of animal dermatophytes diseases.
Dogs, Cats: Microsporum canis
Horses: Trichophyton equinum
Cattle: Trichophyton verrucosum
Birds: Trichophyton gallinae
What is often used to diagnose tineas (eg. microsporum)?
Wood’s lamp
- ‘black lamp’
- wavelength of 365nm
