Lecture 16 Moulds and dermatophytes Flashcards
What are the general properties of Aspergili spp
True hyphal fungi which have branching septate fungi and form conidiophores (asexual sporing bodies). They have rapid aerial growth. They are common soil inhabitants, decompose organic matter and spores are present in dust and air
What is the sequence of events for Aspergillosis if host defences cant stop the fungi
- Spores inhaled
- Development of germ tubes (inflammatory reaction occurs)
- Hyphae grow
- Hyphae invade surrounding tissues
- May see widespread dissemination of fungus
What are the general properties of Aspergillosis (aspergillus spp infection)
Infection usually via respiratory route however can also be through wounds/during surgery.
In healthy hosts disease occurs via mycotoxicosis and allergic aspergillosis
Secondary infections (tissue damage/foreign body) can be keratits, aspergiloma
Secondary infections (immunocompromised) can be CNS, pulmonary or disseminated infections
Describe the general properties of Aspergillus fumigatus
Most common pathogenic species in NZ, causes most disseminated infections in immunocompromised individuals. Conidophores are round with the conidiospores facing downwards. Causes infection of lung, pulmonary infection and allergic disease in immunocompromised usually due to inhalation
How to sample, culture and diagnose Aspergillosis
Samples - Nasal discharge, Bronchial washes and biopsy
Culture - Fresh samples (10% KOH and stain) or culture aerobically on SDA + chloroamphenicol at 37 degrees
Diagnosis - Microscopy, branching septated hyphae with specific spores on fresh samples. Conidiophores on cultured mounts.
What are dermatophytes and general properties
Parasitic moulds which cause ringworm. They use keratin for growth (colonise skin, hair, nails), they are aerobic and are inhibited from growing deeper tissue due to high body temp and lack of iron in deeper.
What are the three types of dermatophytes and give an example for each
Anthrophillic species are parasites to only humans and give a mild disease (Trichophyton rubrum)
Zoophillic species parasites to animals but can be transmitted to humans and give a severe disease (Microsporum canis)
Geophillic species decompose keratin in soil, can be transmitted to humans and give a more severe disease (Nannizzia gypsea)
Describe general properties of Trichophyton rubrum
Dermatophyte in the anthrophillic species, affect the feet, groin, nails and hairless skin. Have small rare macroconidia and numerous microconidia
Describe the general properties of Microsporum canis
Dermatophyte in the zoophillic species, originates from cats. Affects the head and hairless skin. Macroconidia numerous and have thick walls, microconidia usually present.
Describe the general properties of Nannizzia gypsea
Dermatophyte in geophillic species, affects the hairless skin. Macroconidia bean shaped with microcondia rare.
What is the initial process of a dermatophyte clinical infection
Initially, arthrospores (infective spores) sporulate on infected host which can be transferred. Hair invasion common and the spore germinate close to hair follicle and hyphae grow down into follicle. The host shows minimal response.
What is the second process of dermatophyte clinical infection
2 weeks after germination, there is inflammation at lesion (rings). Delayed hypersensitivity to fungal products then occurs which enhances severity of lesions but aids in clearance of lesions
How to sample and culture dermatophytes
Sample - Alcohol wipe, scrape skin at edge of lesion
Culture - SDA + chloroamphenicol at 25 and 37 degrees
How to diagnose dermatophytes
Use microscopy place sample in 10% KOH (breaks keratin) and use microscopes to look for arthrospores and septate branching hyphae
How to differentiate dermatophytes?
Colony appearance
Shape of macroconidia
Specialised trichophyton media
Hair perforation test
