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Laboratory Diagnosis of Fungal Infections PowerPoint Presentation

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This medical PowerPoint presentation talks about fungal infections which can affect various parts of the body, including the skin, nails, lungs, and other organs. The presentation talks about laboratory diagnosis of fungal infections.

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Published on : Mar 31, 2023 | Views : 1976 | Downloads : 1

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Slide 1-

Laboratory Diagnosis of Fungal Infections
Slide 2-

Learning Objectives Review classification & general properties of fungi Discuss the modes of collection & transportation of clinical specimen/s in suspected fungal infection Describe how medically important fungi are identified by microscopic, cultural & serological methods
Slide 3-

Review - Fungal Infections/ Mycoses Superficial mycoses: 2 types: surface and cutaneous mycoses Skin, hair & nails. Deep mycoses: 2 types: subcutaneous & systemic mycoses Range from a symptomatic infection to fatal disease Opportunistic mycoses – mostly systemic involvement
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(a) Superficial Mycosis Clean the part with 70% alcohol Collect the material in a sterile paper or a sterile petridish to - Allow drying of the specimen Reduce bacterial contamination Maintain viability
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(a) Superficial Mycosis Dermatophytic lesion (Ringworm) – spreads outward in a concentric fashion with healing in the center – scrape outwards from the edge of the lesion with a scalpel blade or use Cellophane tape Scalp lesion – scraping with a blunt scalpel, including hair stubs, scales & contents of plugged follicles. Onychomycosis – stop antifungals one week prior to collection Mucosal scrapings
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(b) Subcutaneous Mycosis Scrapings or crusts from the superficial parts of lesions Pus aspirates Biopsy
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(c) Systemic Mycosis Pus Biopsy Feces Urine Sputum CSF Blood Scrapings or swabs from the edge of lesions.
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Collection & Transport of specimen Skin, Hair & Nail Taken for dermatophytic infections Hair – plucked with forceps Tissue, BM & Body fluids Tissues – grind or mince before culturing Body fluids – centrifuge & use sediment for culture Urine – centrifuge & use sediment for culture
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27.05.09 Phase I/ Module VII Laboratory Diagnosis Direct examination Fungal culture Serological tests Skin tests PCR & other molecular methods
Slide 10-

1. Direct Examination Very decisive in the diagnosis of fungal infections Wet mounts Slide & tube KOH mounts – 10 to 20% KOH – digests protein debris, dissolves keratin. DMSO can be added to KOH to hasten clearing in skin scrapings & nail clippings Calcofluor white – fluorescent stain – excellent morphology of pathogenic fungi India ink – capsulated fungi
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27.05.09 Phase I/ Module VII CFW – yeast form of Blastomyces KOH - Aspergillus India ink - Cryptococcus
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27.05.09 Phase I/ Module VII 1. Direct Examination Gram stain – fungi are gram positive Histopathology Superficial infection – acute, subacute or chronic dermatitis with folliculitis Subcutaneous & systemic infections – granulomatous reaction with fibrosis or pyogenic inflammation Routine stain – Hematoxylin & Eosin (HE)
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27.05.09 Phase I/ Module VII 1. Direct Examination Histopathology Special stains – PAS (Per Iodic acid), GMS (Grocott Gomori Methanamine Silver), Mayer’s mucicarmine, Gridley’s stain Fluorescent- antibody staining To detect fungal Ag in clinical specimen such as pus, blood, CSF, tissue sections Adv – can detect fungus even when few organisms are present
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27.05.09 Phase I/ Module VII 2. Fungal Culture Sabouraud Dextrose Agar (SDA) Contains 2% dextrose, antibiotics (gentamicin, chloramphenicol) and cycloheximide Selective media Corn meal agar (CMA) – sporulation, chlamydospore formation Bird seed agar – cryptococcus, forms brown colonies Brain Heart Infusion (BHI) agar – dimorphic & other fastidious fungi
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27.05.09 Phase I/ Module Corn Meal Agar Bird Seed Agar
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2. Fungal Culture Temperature requirement Majority of fungi – 37°C Superficial mycosis – 30°C Dimorphic fungi – 25°C & 37°C Incubation time At least 4 weeks Usually positive cultures are obtained in 7-10 days Candida & Aspergillus - 24 to 72 hrs
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2. Fungal Culture Specimens should be cultured on agar slants: Safe Require less space More resistant to drying during prolonged incubation Blood cultures should be inoculated in to biphasic blood culture bottles
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27.05.09 Phase I/ Module VII Dr Ekta Interpretation of Fungal Culture Isolation of an established pathogen like H. capsulatum or C. neoformans – evidence of infection Isolation of commensal or opportunistic fungi like Candida or Aspergillus – consider following points: Isolation of same strain in all culture tubes Repeated isolation of same strain in multiple specimens Isolation of same strain from different sites Immune status Serological evidence
Slide 19-

Identification of fungal cultures Colony morphology – colour, texture, pigment production
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Identification of fungal cultures Fungal morphology under microscope – using Lactophenol Cotton Blue (LPCB) stain Composition of LPCB Lactic acid - preserves fungal structure Phenol – kills any live organism Glycerol – prevents drying Cotton blue – imparts blue color to structures
Slide 21-

Identification of fungal cultures Special culture techniques – to see sporing structures & spore arrangement, CHROM agar for candida sps. Biochemicals – ability to assimilate carbon & nitrogen, sugar fermentation
Slide 22-

C.tropicalis C.krusei C.albicans CHROM Agar
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Serology Detection of Ag or Ab in serum or body fluids Ab detection: Diagnosis of systemic & subcutaneous mycoses Assess prognosis of the disease Assess response to treatment Ag detection: Early stages of infection In patients with impaired immunity
Slide 24-

Serological tests used in Medical Mycology Agglutination Immunodiffusion – most widely used Counter immunoelectrophoresis (CIEP) Indirect fluorescent Ab detection ELISA, RIA Delayed hypersensitivity reaction
Slide 25-

Other Methods PCR – Polymerase Chain Reaction RFLP - Restriction fragment length polymorphism Protein electrophoresis Nucleic acid probes