Model Answers Microbiology Written examinations 2007 - RCPA

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Eyes Corneal scrapings – fungal keratitis Aqueous vitreous humour Tissue biopsies of any kind E.g. disseminated disease Brain Adrenals Thyroid Blood cultures Candidemias or fungemias How and why Media SAB (+ chlor, gent) 25-30C SD (SAB + cycoheximide) = MYCOSEL or (actidione) + (chlo + gent) 25- 30C DTM = (chlo + gent + cycl) 25-30C SAB without antibiotics (may use for tissues from sterile sites) Chromogenic agar Dixons or overlay with olive oil for M.furfur from blood and occas skin but generally not indicated as microscopy sufficient from skin – 37C Set up in tubes to prevent drying as media held 3-4 weeks Avoid opening lids unless growth to prevent contamination Sporing for microscopy OA SACHs PDA – slide cultures/species etc CMA Basic techniques Macroscopic description of colonies Colour – surface reverse etc Appearance Microscopy from sample Hyphae – hyaline Hyphae – pigmented – T.nigra and other demateaciuos fungi Spores Yeast cells Pseudohyphae Copper pennies (Chromo) – SAB 28 Spaghetti meat ball – M.f Microscopy of colonies Microconidia Macrocondidia Chlamydospores Other techniques Dimorphism demonstration: Mycelial conversion at 28 to Yeast at 37 Exoantigen test – Histoplasmosis Differential temps of incubation Canavanine to speciate Cryptococcus – gattii v neoformans: association with HIV and prognosis
Bird seed – to confirm Crypto Ectoag test e.e. confirmation of culture Histoplasmosis esp when dimorphism difficult Vitek or API if not conclusive for yeast identification Details Skin and subcutaneous infections Specimens Scraping Hair Nails Biopsy tissue Diseases: Superficial: Pityriasis Versicolor (Malazzesia, Tinea Nigra) – Dixons Cutaneous: Dermatophytes – onychomycosis, tinea capitus and tinea corporis/cruris/pedis Subcutaneous: Sporo, Chrom, opportunists (Coelomycetes etc) traumatic implantation Collection: Scrapings, clippings, hair – adequate specimen an issue Microscopy calcofluor white/Evans blue in glycerol KOH, Calcofluor, - hyphae (allows terbinafine on PBS), spaghetti and meatballs = Malazessia furfur Culture media: SAB, SD, DTM Incubation 28C Duration 3 weeks Identification Edothrix, Ectothrix Anthropophilic, Zoophilic, Geophilic – management/source of infection Infection control issues New innovations: PCR Subcutaneous infections: Sporo – S.schenkii (dimorphism) Chromoblastomycoses o Cladiophilaophora grows on clclo 37 o Fonseca Systemic infections with skin manifestations Often grow on the MCS blood agar at 37C e.g Fusarium Respiratory Respiratory Grow on routine bacto plates – normal flora: SAB (ABS) 25-30C, SD 25- 30C + BHI (ABS0 (35) Nocardias on BHI Aspergillus spp, Scedospoium prolificans apiosperman Cryptococcus sensitive to cycloheximide Note lab safety issues: white fluffy fungi esp from resp tract but other tissues as well- arthroconidia of Coccidioides etc lab hazard DFA/silver staining/toluidine blue/PCR with quantification on respiratory specimens in immunosuppressed patients who have ground glass appearance suggestive of PCP (NB also stain with calcoflur)
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Model Answers Microbiology Written examinations 2007 - RCPA

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