Clinically Important Fungi 2024/25 - Student PDF

CLINICALLY IMPORTANT FUNGI. A.P Dr Salwani Ismail LEARNING OUTCOMES 1. Classify clinically important fungi 2. List the examples of fungi of medical importance 3. Describe the laboratory characteristics of the fungi. INTRO  ~80,000 species of fungi have been described,...

CLINICALLY IMPORTANT FUNGI. A.P Dr Salwani Ismail LEARNING OUTCOMES 1. Classify clinically important fungi 2. List the examples of fungi of medical importance 3. Describe the laboratory characteristics of the fungi. INTRO  ~80,000 species of fungi have been described, but  < 400 species are medically important, and  < 50 species cause > 90% of the fungal infections of humans & other animals. INTRO  Mycoses/mycosis – fungal infections/infection  Fungi origin – exogenous or endogenous  Most pathogenic fungi are exogenous, their natural habitats are:  Water  Soil  Organic debris e.g birds droplet/feces etc  The mycoses with the highest incidence e.g candidiasis & dermatophytosis are caused by fungi that are part of the normal flora (endogenous) GENERAL PROPERTIES OF FUNGI. FUNGI GROW IN 2 BASIC FORMS: Mold Yeast  MOLD  Mold – growth occurs by production of multicellular filamentous colonies.  Colonies consist of hyphae (branching tubular structures ~2-10 µm in diameter which is usually divided into cell-like units by cross walls called septa)  The total mass of hyphae is termed a mycelium. Aspergillus flavus  MOLD Aspergillus niger Image of Aspergillus flavus hyphae (400x) in hand tissue of a patient stained with Haemotoxylin eosin. YEAST  Yeast: single cell, usually spherical to ellipsoid in shape and varying in diameter from 3-15 µm.  Most yeast reproduce by budding.  Some spp. produce buds that characteristically fail to detach & become elongated (pseudohyphae) Gram staining of Candida albicans YEAST pseudohyphae Pseudohyphae of Candida albicans Scanning electron micrograph (SEM) of Candida albicans  Under standardized growth conditions in lab, molds produce colonies with characteristic features: Pigmentation – black, green etc Growth rate – fast (24-48 hours) or slow growing fungi (4 wks) Texture -powdery or fuzzy  Yeast colonies are usually soft, opaque, 1- 3mm in size and cream-colored. MOLD VS. YEAST COLONIES Aspergillus flavus (mold) Candida spp. (yeast)  Some species of fungi are dimorphic & can grow as a yeast or mold depending on the environmental condition DIMORPHIC FUNGI DIMORPHIC FUNGI  Thermally dimorphic fungi Culture at 35-37°C – yeast-like fungi Culture at 25-30°C – filamentous fungi/mold  Clinical disease Systemic mycoses Opportunistic mycoses Subcutaneous mycoses DIMORPHIC FUNGI  Sporothrix schenckii  Blastomyces dermatitidis  Coccidioides immitis  Penicillium marneffei  Histoplasma capsulatum  Dimorphic fungi Sporothrix schenckii at 37°C Sporothrix schenckii at 25°C FUNGAL CELL WALL  All fungi have an essential rigid cell wall that determines their shape.  Composed of: Carbohydrate layers (long chain polysaccharide) Glycoprotein Lipid FUNGAL CELL WALL (CONT.)  Cell wall: Mediates attachment of the fungus to host cells Activates the complement cascade & provoke an inflammatory reaction Elicits cellular & humoral immune response FUNGI CLASSIFICATION  Fungi are classified into 4 major phyla: Zygomycota Ascomycota human pathogen Basidiomycota Chytridiomycota ❖ Ascomycota – the largest phylum, which includes >60% of the known fungi and ~ 85% of the human pathogens ZYGOMYCOTA ZYGOMYCOTA  Sexual reproduction results in a zygospore; asexual reproduction occurs via sporangia.  Vegetative hyphae are sparsely septate.  Class: Zygomycetes  Species: Rhizopus spp., Mucor spp., Absidia spp., Philobolus spp.  Disease: Zygomycosis (e.g mucormycosis) Zygospore of Rhizopus spp. MUCORMYCOSIS  Causative agent: Mucor spp.  Infection may involve sinuses, brain, lungs, oral, gastrointestinal tract, skin, and other organs Oral mucormycosis Skin mucormycosis ASCOMYCOTA ASCOMYCOTA  Class: Ascomycetes  Cause ~ 85% of the human fungal infections  Species: Histoplasma spp, Blastomyces spp, Penicillium spp., Candida spp. Aspergillus spp., Microsporum spp, Trichophyton spp. (e.g Trichophyton rubrum), Saccharomyces spp., Candida spp, Coccidioides spp. Sporothrix schenckii, etc  diseases: histoplasmosis, blastomycosis, candidiasis, tinea capitis/corporis/pedis etc Oral candidiasis ASCOMYCOTA Histoplasma capsulatum Histoplasmosis  Trichophyton rubrum Tinea capitis Tinea unguium/onychomycosis  Trichophyton rubrum Tinea corporis Tinea pedis BASIDIOMYCOTA BASIDIOMYCOTA  Class: Basidiomycetes  Species: Cryptococcus neoformans, Malassezia spp., Trichosporon spp.  diseases: cryptococcosis (e.g cryptococcus meningitis etc)  CRYPTOCOCCUS NEOFORMANS  Yeast characterized by a thick polysaccharide capsule  Found very large numbers in dry pigeon feces CRYPTOCOCCUS NEOFORMANS  Infection follows inhalation of the yeast cells  Primary pulmonary infection (pulmonary cryptococcosis) maybe asymptomatic or mild flu-like illness – in immunocompetent  In immunocompromised host, yeast disseminated to other parts of the body esp CNS, causing cryptococcal meningoencephalitis or cryptococcal meningitis INVESTIGATIONS OF CRYPTOCOCCAL MENINGITIS  FBC  ESR/C-reactive protein  CXR  sputum cultures (with special attention towards obtaining appropriate fungal cultures) should be sent.  Blood cultures are positive for cyptococci in approximately 66% of cryptococcal meningitis cases.  HIV testing  cerebral spinal fluid (CSF) analysis – cell (WBC) count, CSF protein & glucose levels, India ink staining, CSF cryptococcal antigen detection and fungal culture.  CSF studies characteristically show an elevated white blood cell count (WBC) with a predominant lymphocytosis, elevated protein levels and distinctive low glucose levels.  India ink – yeast cells (oval in shape cells) with thick polysaccharide capsule TREATMENT  Antifungal agent - Amphotericin B in combination with flucytosine LAB DIAGNOSIS OF FUNGI INFECTION  Microscopic examination  Culture  Identification test  Sensitivity test LAB DIAGNOSIS OF FUNGI INFECTION  Microscopic examination. Saline wet mount Lactophenol cotton blue (LPCB) Potassium hydroxide (KOH) preparation Gram stain e.g Candida albicans India Ink preparation – Cryptococcus neoformans Other stains MICROSCOPIC EXAMINATION – Candida albicans Wet mount Gram staining India ink – Cryptococcus neoformans Light microscopy of Aspergillus spp with lactophenol cotton blue (LPCB) stain cultured from burn wound. FUNGAL CULTURE  Primary fungal media Saboraud Dextrose Agar (SDA) Saboraud Dextrose Agar with cycloheximide and chloramphenicol (SDA-C&C) Brain Heart Infusion Agar with Blood (BHIAB) INCUBATION TIME  Some fungi mature within 3 to 4 days and others 3 to 4 weeks.  Growth rate depends on temperature of incubation, media used, inhibitors in patients specimens.  Culture for fungus is kept for 1 month before discarded as negative. IDENTIFICATION OF YEAST ❑ Methods include: Microscopic morphology on corn meal-Tween 80 agar Germ Tube production Assimilation reaction Urease production Pigment production API Molecular- PCR AST  As guidance in the choice of anti-fungal drugs  Antifungal Groups & drugs: Polyene – e.g Amphotericin, nystatin Azole - e.g Fluconazole, itraconazole, and ketoconazole. Allylamine and Morpholine - e.g Allylamines (naftifine, terbinafine), amorolfine Antimetabolite - e.g 5-Fluorocytosine  TQ