Mycology
Fungal Media "demystified"
CULTURE MEDIA FOR FUNGI
Clinical specimens are processed promptly and plated on isolation media to recover fungi that may be causing disease. Media and incubation temperatures are selected to allow for the growth of pathogenic and opportunistic yeasts and fungi.
NB. If Histoplasma, Coccidioides, Paracoccidioides, Blastomyces or Penicillium marneffei are suspected, Category 3 Containment is required.
Prototheca wickerhamii
This organism was recovered from a tunnelled CVC of a haemtaology patient. I have never heard of it, so I thought we could summarise it:
Microbiology:
Risks for Candidaemia
- Abdominal surgey
- Broad spectrum antibiotics
- Long lines
- Candida Colonisation
- Pancreatitis
This patients may benefit from treatment - see definitions.
AMH.
Cryptococcus laurentii
Cryptococcus laurentii is an extremely rare human pathogen. This fungus was previously considered saprophytic and nonpathogenic to humans, but it has been isolated as the etiologic agent of skin infection, keratitis, endophthalmitis, lung abscess, peritonitis,meningitis and fungaemia.
Ecology
Candida chromogenic agar
The medium incorporates two chromogens that indicate the presence of the target enzymes:
Antifungal Drugs [overview]
This review on antifungal drugs and their mechanisms of action, can be found HERE.
AMH.
Suspected blood culture contamination problem (Paecilomyces variotii)
We have had multiple occasions of blood cultures "contaminated" with Paecilomyces variotii. This is in keeping with other labs, and was reported by the DoH in Feb '07. It has been suggested that any results should be interpreted with extreme caution, although Paecilomyces is thought to be pathogenic. We will discuss this below.
- Paecilomyces can inhabit soil, decaying plants and food products. Identification is made on the colour of the colony and certain microscopic features. Thermophilicity (growth @50-60oC) suggested Paecilomyces variotii or Paecilomyces crustaceus.
- Paecilomycosis can occur in humans and may be associated with immunosupression. Clinical syndromes include:
- Corneal ulcer, keratitis and endophthalmitis due to contact lens wearing or ocular surgery.
- In the immunospressed, infection may occur by direct innoculation and can involve almost any organ (SSTI, pulmonary, ENT, endocarditis, osteomyelitis, peritonitis, CRBSI).
- Paecilomyces spp can also cause an allergic alveolitis.
- Macroscopically, the colonies can grow in <3 days. Colonies may be flat, powdery or velvety in texture. The colour is initially white, but this colour will change and may indicate the final species.
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Septate hyaline hyphae, conidiophores, phialides, conidia, and chlamydospores are observed. Conidiophores (3-4 µm wide and 400-600 µm long) are often branched and carry the phialides at their tips. The phialides are swollen at their bases and taper towards their apices. They are usually grouped in pairs or brush-like clusters. Conidia are unicellular, hyaline to darkly colored, smooth or rough, oval to fusoid, and form long chains. Chlamydospores are occasionally present.
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Susceptibility:
- Amphotericin B - low MIC
- 5-FC - high MIC
- Fluconazole - high MIC
- Itraconazole/voriconazole - low for Paecilomyces variotii
- Caspofungin - low for Paecilomyces variotii
AMH
