Laboratory
UK SMI notes – Ear Infections.
Type of specimen: Ear swab Middle ear fluid Scraping of material from the ear canal (for fungal infection) Expected organisms Otitis Externa Acute localised otitis externa Staphylococcus aureus Group A Streptococcus furuncle Erysipelas Acute diffuse otitis externa Pseudomonas aeruginosa S. aureus Anaerobes Treatment – topical cleaning of debris. Antibiotics are not useful. Chronic otitis externa Colonisation by Enterobacteriaceae Fungi Treatment […]
SMI: Investigation of whooping cough
Types of specimen Cough plates are not recommended. Selective media It contains blood or charcoal or both, along with selective antibiotic supplements – penicillin, cefalexin or meticillin.It should be able to suppress other nasopharyngeal flora. Meticillin is the least inhibitory, and cefalexin is the most. Cefalexin is the drug of choice for selective media in […]
SMI: Investigation of Throat-Related Specimens
Specimens Throat swab, posterior pharyngeal swab, nasopharyngeal swab, pharyngeal washings, pus aspirate, oropharyngeal swab, throat gargle. Why To investigate upper respiratory tract infection – Pharyngitis, Tonsillitis, Epiglottitis, and Laryngitis. Condition Target organisms Pharyngitis(sore throat) 1. Viral (commonest),2. Group A Streptococcus/ Streptococcus pyogenes,3. Group C/G Streptococcus – Streptococcus dysgalactiae subspecies equisimilis,4. Streptococcus anginosus group,5. Corynebacterium – […]
SMI Summary: Investigation of bone marrow
Because it is an invasive procedure, bone marrow biopsy (typically collected from the posterior iliac crest or the sternum) is rarely used. It’s also proposed that it shouldn’t be done on people who are immune-competent.It may be useful in the diagnosis of infection in immunocompromised patients (HIV, transplant patients, or patients on high-dose steroids), caused […]
SMI (note): Investigation of swabs from the skin and superficial soft tissue infection
Specimen Advice for the users: Safety Processing Gram stain – usually not done unless deep-seated pus from a normally sterile site Plate selection CONDITION PLATES All clinical conditions Blood agarCLED/MacConkey agar Wound swab Selective anaerobic agar with metronidazole disc Pus Fastidious anaerobic, cooked meat broth;then Subculture to blood agar. Cellulitis in childrenHuman bite Chocolate agar […]
Culture media and composition
This is a list of some culture media and their composition. MEDIA SUPPLEMENTS TARGET ORGANISMS ABC plates Alpha-galactosidase Salmonella sp. Alkaline peptone water [pH – 8.6 ± 0.2] NaCl, peptone Enrichment of Vibrio spp. Aztreonam Blood Agar Aztreonam, blood agar base Gram-positive, especially fastidious gram-positive organisms BHI Broths Calf brain and beef heart infusion solids, peptone […]
Catalase test
This test detects the catalase enzyme present in most cytochrome-containing aerobic and facultative anaerobic bacteria. The catalase enzyme converts hydrogen peroxide ( H2O2 ) to oxygen and water. This reaction can be observed as the rapid formation of bubbles. The reaction 2 H2O2 → 2 H2O + O2 Catalase positive organisms Gram-positive organisms Staphylococcus, Micrococcus,Aerococcus urinae (Note: Aerococcus […]