Mycology (Dimorphic Fungus, Tinea, Mycetoma, Candida)

Mycology, which is the study of fungi, is an important topic in microbiology. Fungal infections are becoming increasingly common, making mycology a highly relevant topic for the NEET PG exam.

Moreover, fungal infections can often mimic bacterial or viral infections, which makes it all the more essential to have a strong understanding of mycology in order to avoid misdiagnosis.

Let’s learn more about this important NEET PG exam topic of microbiology through this blog.

Morphological Classification

• Yeast - Cryptococcus neoformans
• Yeast like - Candida (Yeast, yeast like hyphae, pseudo hyphae)
• Molds - Aspergillus, Rhizopus

Dimorphic Fungus

• Mold– 25° C
• Yeast - 37° C

Dimorphic Fungal Disease

• Histoplasmosis            
• Sporotrichosis
• Blastomycosis
• Coccidioidomycosis
• Paracoccidioidomycosis
• Penicilliosis

Types Of Spores

Sexual Spores

• Zygospores
• Ascospores
• Basidiospores

Asexual Spores

• Arthroconidia
• Blastomyces
• Chlamydospores

Based On Location

Superficial Mycosis

• Tinea versicolor
• Tinea nigra
• Dermatophytes

Subcutaneous Mycosis

• Mycetoma
• Rhinosporidiosis
• Chromoblastomycosis
• Sporotrichosis

Systemic Mycosis / Deep Mycosis

• HSBCP² (All dimorphic fungal diseases)
• Candida
• Cryptococcus

Lab Diagnosis

Culture Media

• SDA (Sabouraud’s dextrose agar) → Universal fungal culture media
• pH = 5.4 – 5.6

Fungal Stains

• Negative staining (Eg: Cryptococcus) capsule
  • Indian ink stain
  • Mucicarmine stain
  • Nigrosin
• GMS (Gomori Methenamine Silver)
  • Eg: Pneumocystis Carinii (Green colour)
• LPCB (Lactophenol Cotton Blue)
• H&E (Haematoxylin + Eosin)
• Calcofluor white – Fungal Fluorescent stain  

Also Read: HELMINTHOLOGY : Structure, Classification, Growth, and Development : NEET PG Microbiology

Tinea

T. Versicolor (Pityriasis Versicolor)

• Caused by Malassezia furfur / M. globosa
• Spaghetti & meatball appearance 
• Fried egg colonies (lipophilic fungus) on SDA
• Golden yellow fluorescence

T. Nigra

• Exophiala werneckii

Dermatophytes

• Lab Diagnosis
  • Culture growth on SDA + LPCB

T. Capitis

• Favus
  • T. Schoenleinii(Trichophyton)

• Kerion
  • Painful boggy swelling
  • T. Mentagrophytes, T. Verrucosum

T. Cruris

• Dhobi itch or jock itch

T. Pedis

• Athlete’s foot 

MYCETOMA (Madura foot)

• Triad
  • Sinus
  • Swelling
  • Granules (Discharging)

Rhinosporidiosis

• Caused by Rhinosporidiumseeberi
• Aquatic protist – protozoa
• B/ L nasal polyp
• On Polyp biopsy 
  • Spherule
  • Within spherule there are endospores

• Non cultured on SDA
• Treatment – Surgical removal

Chromoblastomycosis

• Colourful fungus
• Dematiaceous fungus
• Eg
  • Alternaria
  • Bipolaris
  • Curvularia
  • Phialophora
  • Cladosporium
  • Exophiala werneckii

• Thorn prick / wood worker → Verrucous lesion
• On tissue biopsy + H & E staining
  • Medlar bodies
  • Brown coloured sclerotic bodies
  • Copper penny / muriform appearance

Sporotrichosis

• Sporothrix schenckii
• Rose gardener’s disease
• Lymphocutaneous spread
• Increased incidence in and around valentine’s day

• Dimorphic
  • Mold-Flower like sporulation
  • Yeast- Cigar shaped yeast cell (Narrow based budding)
  • Asteroid yeast cell

Histoplasmosis

• Darling’s Disease
• Mimics TB (when involves lungs)
• Histoplasma capsulatum

• Aerosols - Pulmonary involvement
• Blood 
• Visceral involvement
• Mold - Tuberculate macroconidia
• Yeast - Narrow based budding

Blastomycosis

• North American’s disease / Gil Christ disease
• Yeast cell → Figure of ‘8’ appearance or broad-based budding yeast cell
• Can happen in HIV + person

Coccidioidomycosis

• Caused by coccidioides immitis
  • San Joaquin Valley Fever 
  • Desert Rheumatism
• Mold-Arthroconidia arrangement (Rectangular)
• Yeast - Spherule with endospore

Paracoccidioidomycosis

• South American disease / LUTZ mycosis
• Yeast cell - Mickey mouse appearance / Mariner’s wheel appearance

Penicilliosis

• Penicillium marneffei
• Found in HIV +ve
• Brick reddish colour pigment
• Brush conidial arrangement

Candida

C. Krusei

• Inherent resistant to azoles

C. Auris

• Worldwide infection in Immunodeficient individuals

Candida Albicans

• Diseases
  • Oral thrush
  • Oesophageal candidiasis
  • Vaginal candidiasis (Curdy white discharge)
  • Onychomycosis (Nail folds)
  • Candidemia
  • Candiduria
  • Meningitis

• Predisposing factor 
  • Steroids use,immune deficient individuals, neutropenic patients > HIV +ve
  • CMC (Chronic mucocutaneous candidiasis) (T cell disorders)

• Lab Diagnosis
  • Cultured on SDA → creamy & pasty colonies
  • SDA-cannot differentiate Cryptococcus and candida
  • Chrome agar → colourful fungus
  • PCR for C. Albicans
  • For invasive candidiasis → β D glucan assay

Cryptococcus

• Trust yeast
• In immune deficient (HIV +ve)
• Transmission by 
  • Pulmonary infections
  • Blood 
  • Meninges (Meningitis)

C. Meningitis

• Lab Diagnosis
  • Blood & CSF
    • Cultured on SDA
    • Smooth mucoid creamy colonies (SDA cannot differentiate Cryptococcus and Candida)
  • Phenyl oxidase enzyme in Cryptococcus – responsible for melanin production
  • On Niger seed agar – Brown black colonies are seen
  • Latex card agglutination Test for Cryptococcal Antigen
  • PCR for C. Neoformans
  • Capsulated organism (Polysaccharide) - Indian ink staining (negative stain)
  • Polysaccharide capsule → Virulence factor

• Treatment
  • DOC Cryptococcal meningitis - Lysosomal amphotericin B (LAMB)+ Flucytosine

Zygomycetes

• Seen in Terminally ill patients

• Rhizopus
• Absidia
• Mucor
  • Rhinocerebral Zygomycosis is a fulminant disease
• Lab Diagnosis
  • Tissue biopsy - H & E stain
    • Aseptate hyphae
    • Obtuse angled
  • Biopsy material on SDA
  • Culture growth + LPCB

Different Zygomycetes

• Absidia – Inter nodal rhizoids arrangement
• Mucor - No rhizoids

Mucormycosis

• Mucormycosis is commonly seen in
  • DM
  • Frequent blood transfusion
  • Chronic dialysis

Aspergillosis

• Common in DM, Immunodeficient

A. Fumigatus

• Leads to allergic bronchopulmonary aspergillosis
• Associated with aspergilloma (Fungal balls)
• Oculomycosis
• Otomycosis
• On SDA Greenish colour colonies in SDA

A. Niger

• Blackish crust from ear
• On SDA - Black coloured colonies

A. Flavus

• produces aflatoxin which leads to hepato cellular Carcinoma
• Lab Diagnosis: On Tissue Biopsy + H & E Staining
  • Septate hyphae
  • Dichotomous branching
  • Mostly Angle 45º

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