Laboratory diagnosis of fungal disease- selective overview

Organism Microscopy Culture and identification Non-culture methods
General Histopath PAS & silver stains etc.

K0H with Parker ink (skin scrapings/nails)

SAB (Saborauds dextrose agar) medium +/- antibiotics +/- cycloheximide

For other media, see here.

Blue thymol blue sticky tape preparation from cultures for examining hyphae and fruiting structures

MALDI-TOF for ID

Invasive fungal disease: 1-3 Beta-D-Glucan assay (serum) – broad spectrum but not incl. Cryptococcus

Candida albicans and other similar species Characteristic yeast shapes larger than bacteria; appear Gram positive Colonies with ‘feet’ (C. albicans)

Chromogenic candida agar – usually sufficient for ID. Several types.

Yeast sugar assimilation panels e.g. API , VITEK etc

 

 

C. neoformans

C. gattii

India ink preparation for capsule (CSF)

NB. capsule production media dependent

Presumptive: capsule+yeast= Cryptococcus (no other species has a capsule)

Urease positive

Bird seed agar – pigmented colonies = Cryptococcus

CGB medium- (L-Canavanine, glycine, 2 bromthymol blue agar) distinguishes C. gattii from C. neof.

Crypto antigen lateral flow assay (serum/CSF)

 

IF serotyping of isolates- research only

Aspergillus species Histopath – narrow septate hyphae; acute angle branching Culture appearance- pigmentation

Species ID by sticky tape preparation

Galactomannan EIA  (serum, BAL)

Serum precipitins used in ABPA Dx

 

Pneumocystis jirovecii(PJP) Bronchial lavage / induced sputum – IF / silver / Giemsa stains Usually a clinical diagnosis

No culturable

 

PCR more sensitive than IF

Histopathologic Diagnosis of Fungal Infections in the 21st Century : excellent overview- invasive fungal infections are often recognised only by histopathologists post mortem! Also this slide set : https://www.slideshare.net/appyakshay/fungus-in-histopathology

Cryptococcal serum antigen screening for HIV positive patients– previous posting.  This ICT has excellent sensitivity and specificity for crypto antigen detection.

India ink preparation                                      Gram stain of Candida species

About mdjkf

Microbiologist and Infectious Diseases Physician
This entry was posted in Fungi, Module-Mycology. Bookmark the permalink.

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