Micro 5: Fungal infections Flashcards
What are examples of yeast?
Candida, Cryptococcus, and Histoplasma (dimorphic)
What are examples of moulds?
Aspergillus, Dermatophytes, agents of mucormycosis
What is a dimorphic fungi?
Some fungi are dimorphic and can change between being yeast and moulds
What is the most common yeast?
Candida
How does Candida look and how does it replicate?
They form individual cells (a bit like bacteria but much bigger). They replicate by budding. Candida grow in colonies (a bit like bacteria).
What is Candidiasis and what can it affect?
It is a primary or secondary mycotic infection caused by members of the genus Candida. It can affect the mouth, perineum, scalp, skin, vagina, nails, lungs and GI tract.
How can Candidiasis become systemic?
It can become systemic as in septicaemia, endocarditis and meningitis.
Who is more likely to get systemic candida infections?
VLBW infants are more likely to get systemic candida infections
What treatment may infants with systemic candida infection require?
They may require fluconazole and nystatin prophylaxis.
Who is more likely to get invasive candidiasis?
- Immunocompromised patients are more likely to get invasive candidiasis.
- Patients on ITU with lots of lines in (e.g. central lines) are also at risk because Candida is very good at forming biofilms and colonising prosthetic material.
- More common in people receiving TPN.
- Immunocompetent people can get candidiasis receiving antibiotic therapy because the antibiotics will kill the commensals
Where is candidiasis found?
This disease is found world-wide
What aetiological agents cause candidiasis?
Candida albicans (MOST COMMON), Candida glabrata, Candida krusei, Candida tropicalis, and many others. All of them are ubiquitous and occur naturally in humans.
Are the yeast causing candidiasis sensitive to antifungals?
Candida albicans is sensitive to all the first line antifungals. On the other hand, C. glabrata and C. krusei are resistant to a lot of first-line drugs.
Why aren’t cultures ideal to screen for candidiasis/fungal infections?
Early identification of the fungal guides treatment. Candida albicans forms a germ tube whereas the other types will not. Yeasts take a lot longer than bacteria to grow colonies so doing cultures will take much more time. This is why an alternative identification system is needed.
What organs does systemic candidiasis involve?
Can involve the liver and the spleen. Candida can also affect the eyes causing endophthalmitis.
How does generalised candidiasis present in babies?
This is often secondary to seborrhoeic dermatitis. It can often affect the folds of the skin - called intertrigo. (In immunocompromised patients candida can also invade tissues).
How is candida diagnosed?
Swabs, blood cultures for candidaemia using a selective agar plate (Sabourard agar), Beta-D Glucan assay and imaging
Why must you use a selective agar plate for Candida?
Candida is often outcompeted in cultures because bacteria grow more quickly. So, a selective agar plate that is impregnated with antibiotics is usually used (Sabouraud agar). Therefore, if you are suspicious that someone has a Candida infection then you should say so when you send the sample. Grows in about 48 hours.
What is the management for candidiasis?
Treat for at least 2 weeks of antifungals from the first negative blood cultures. Echo and fundoscopy (look for endocarditis and endophthalmitis). Echinicandins are used empirically and for non-Candida infections. Fluconazole is still effective for Candida albicans. May need to use a certain type of antifungal because of its pharmacokinetics/pharmacodynamics
Echinicandins don’t penetrate well into the CNS, what can you use instead?
Ambisome
What is cryptococcus?
A chronic, subacute to acute pulmonary, systemic or meningitic disease, initiated by the inhalation of a fungus. Primary pulmonary infections are usually subclinical.
What does cryptococcus show a predilection for?
On dissemination, the fungus usually shows a predilection for the CNS
What treatments can be used for cryptococcus, and what is it resistant to?
It looks like a yeast and will stain similarly but it is inherently resistant to echinicandins. It is susceptible to fluconazole and amphotericin. Treatment of choice: ambisome
What is the aetiological agent for cryptococcus?
Cryptococcus neoformans
Who is susceptible to cryptococcosis?
Patients with impaired T cell immunity; AIDS patients with very low CD4+ counts (typically <200 m/L) - second most common cause of death in AIDS; patients taking immunosuppressants for solid organ transplant also have 6% lifetime risk.
What happens in Cryptococcus neoformans var. gatii and who gets it?
It causes meningitis in apparently immunocompetent individuals in tropical latitudes (especially SE Asia and Australia). There is a high incidence of space-occupying lesions in the lung and brain. Recent outbreak in Vancouver Island.
What does Cryptococcus neoformans var. gatii have an increased resistance to?
Increased resistance to amphotericin B.
What is the life cycle of Cryptococcus?
The spores are ubiquitous. (Originating from eucalyptus tree and bird excreta?) It will be inhaled and then, in immunocompromised patients, it will disseminate. There is a predilection for the central nervous system.
What is used to stain cryptococcus and how does it look like under microscopy?
Cryptococcus has a very distinct capsule around the yeast. India ink is used to stain for Cryptococcus. The ink will stain everything black except for the capsule around the yeast. The capsule is NOT always present (if the organism is not under any form of stress it will not need the capsule (e.g. in blood cultures)). India ink is not used very frequently anymore.
What has replaced ink staining to detect cryptococcus?
Instead, an enzyme immunoassay (EIA) to look for components of the capsule are used now. (Cryptococcus can grow in culture but the antigen test is much quicker).
