Review/Oorsig Volume 22, Issue 01 - Page 19

Volume 22 • Issue 01 • 2018 • • Place wrapped slides in a sealed sample envelope to avoid formalin-fume contamination. Formalin-fume contamination severely compromises the efficacy of the FAT Smear Examination • • • • • • Examine Diff-Quick stain first to determine if any clostridial-like organisms present, if so estimate numbers. Only 4 species of clostridia available in the FAT assay (Clostridium chauvoei, Clostridium novyi, Clostridium septicum) Must correlate FAT results to all other assays performed. Avoid basing diagnosis solely on the FAT result. False negative FAT results 1. Poor bacterial recovery (reason why examine Diff-Quick slide 1st) 2. Low bacterial load at sample site, pathology initiated by clostridial toxins False positive results 1. Post mortal proliferation 2. Concurrent Clostridium perfringens myositis Anaerobic culture • • • • • • A block of subcutaneous and/or muscle tissue/fluid/charcoal swab is collected from the site where the impression smears weere prepared. There was no significant difference in the ability to isolate clostridia between these sample types. All samples need to have oxygen excluded as soon as possible For subcutaneous / muscle tissues, block sample should be a minimum of 4cm3, as this favours the maintenance of anaerobic conditions at the centre of the block. Place tissue block in a sample envelope which is then folded to exclude oxygen and sealed. Fluid samples are collected into a sterile syringe, air is then expelled and the needle • • bent back on itself or plugged. When using charcoal swabs ensure that the swab is inserted deep into the transport medium. Solid tissue samples should be transported at 4ºC, while fluids should not be sent on ice as oxygen dissolves better in fluids at low temperatures. Histopathology • • • • • • Artefactual changes as a consequence of asynchronous contraction of muscle following immersion of muscle tissue in formalin can interfere with interpretation of interstitial emphysema or oedema. Collect block of subcutaneous tissue / muscle, that must not exceed 1cm in thicknes