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Aim of the test
• Isolate and identify aerobic and anaerobic pathogenic organisms in pus specimen.
• Types of specimen: • Swabs from the infected area or aspiration
from deep wounds. Swabs in anaerobic transport media for the isolation of anaerobes.
Criteria of specimen rejection
• Inappropriate specimen transport device; mislabeled specimen; unlabelled specimen.
• Dried samples and specimen received after prolonged delay (usually more than 72 hours).
• Specimen received in expired transport media
Pathogen and commensals
Specimen collection • Pus from abscess is best collected at the time the
abscess is incised and drained.• Using sterile technique, aspirate or collect from
drainage tube up to 5 ml of pus, transfer to sterile container.
• If pus is not being discharged use sterile cotton wool swab to sample from the infected site.
• Extend the swab deeply into the depth of the lesion.
• Immerse the swab in container of transport medium
• Label it and send to the laboratory as soon as possible.
• Quantity of specimen: sufficient amount on swab, or aspiration in transport media or syring
• Time relapse before processing the sample: 30 min.
• Storage: Maintain specimen swab at room temperature. Do not refrigerate.
Culturing procedure• Streak one blood agar plates, one chocolate,
MacConkey and inoculate thioglycollate broth tube.
• Gram stain to check the presence or absence and if present the type or types and the predominant organisms.
• Turn around time: • Gram stain results should be available 1 hour
after specimen receipt. • Isolation of a possible pathogen can be expected
after 2-3 days. • Negative culture will be reported out 1-2 days
after the receipt of the specimen
Specimen processing
Post specimen processing
• Interfering factors: • Patient on antibiotic therapy. • Improper sample collection.
• Result reporting: • Report Gram stain finding as an initial report. • Report the isolated pathogen/s and its
sensitivity pattern as a final report.
Additional information
• Contamination of the specimen with normal miceobiota is one of the major obstacles in obtaining good results.
• Care should be taken to avoid contaminating the specimen with normal commensals.
• This could e accomplished by swabbing superficial infected wounds with 70% alcohol.