Pus - microscopy and culture

Last updated: Sunday, 28, May, 2006

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Item Process
Specimen

Aspirate from collection, abscess or wound; biopsy of abscess wall. The specimen should be collected in a sterile container.

Pus should always be aspirated, if possible, rather than collecting a wound swab.

Swabs from a draining wound or sinus are frequently contaminated with normal flora from skin, mucous membrane.

Pus or wound swab (in transport medium) should be transported immediately to the laboratory.

Biopsy of abscess wall or adjacent tissue may increase the yield, especially in chronic infection.

Method

Gram stain for microscopy.

Bacterial culture for aerobes and anaerobes.

Stain for acid fast bacilli and/or culture for mycobacteria and fungi is performed only if specifically requested.

Application

Identification of pathogenic organism(s) to enable selection of the most appropriate management.

Interpretation

Presence of neutrophil polymorphs and bacteria in Gram stains of uncontaminated aspirates or swabs identifies likely bacterial infection.

Acid fast bacilli in pus or adjacent tissue biopsy suggests mycobacterial infection.

Nocardia spp may be acid fast with modified staining techniques.

Yeasts or hyphae suggest fungal infection.

See also Wound infection, Ear swab, Genital swab, Conjunctival swab/fluid.

Reference

Gill VJ et al. In: Mandell GL et al eds. Principles and Practice of Infectious Diseases. 6th ed. Churchill Livingstone 2005.