Effective Date: 
Mon, 08/19/2013
Fri, 03/24/2017

Purpose and Scope:

Wound infections may be due to a variety of organisms, but are most commonly associated with S. aureus, beta-hemolytic streptococci, P. aeruginosa and enteric Gram negative bacilli. The presence of squamous epithelial cells may indicate that the specimen is superficial and therefore the organisms isolated may not reflect the true etiology of the infection.

Reagents and Supplies:

5% Sheep Blood agar plate
MacCONKEY agar plate
CNA agar plate
Disposable sterile loops
37 C incubator


Specimen Collection and Transport

Specimens should be collected using a clean, sterile swab and sent in Amies transport medium.

If anaerobic culture is requested, an anaerobic swab placed in an anaerobic transport tube must be collected. If a delay in transport or processing is anticipated, the aerobic swab should be kept at 4 C. If both an aerobic and anaerobic swab are received, both swabs should be kept at room temperature until processed.

Anaerobic swabs, bite wound swabs, ear swabs and eye swabs are to be sent to Quest Diagnostics. Cultures received on Fridays or cultures that require further workup on a Friday are sent to Quest Diagnostics.

Processing of Specimens

 Culture: Media Incubation

Blood Agar (BA)
Colistin Nalidixic Acid Agar (CNA)

Allow plates to come to room temperature before use.

Streak plates for isolation using disposable sterile loop. Incubate 24-48hrs (48hrs if no growth) in 37C incubator.

 Interpretation of Cultures

Examine the aerobic plates after 24 hours incubation. Re-incubate for 24hrs if no growth. Any growth of S. aureus, beta-hemolytic streptococci or Pseudomonas is significant. Enteric gram negative rods and/or enterococci may be significant depending on their number in relation to skin flora and the presence or absence of WBCs on the gram stain.  If Staph aureus is detected, rapid testing for Methicillin Resistant Staph Aureus (MRSA) will be done.

Quantitate the amount of pathogens and any normal skin flora using few, moderate or many estimation. Normal skin flora may include Coagulase negative staph, diptheroids or lactobacillus.

Few = growth only in 1st section
Moderate= growth in 1st and 2nd sections
Many= growth in all sections

Kirby Bauer sensitivities are performed on Staph aureus, enterococci or enteric gram negative rods. If Pseudomonas is detected, sensitivities will be sent to Quest.  If MRSA has been detected, a test for resistance to Clindamycin will be added to the sensitivities.






Textbook of Diagnostic Microbiology, Mahon & Manuselis, 2ndedition, Chapter 27, pages 919-944; Chapter 33, pages 1045-1052; Chapter 35, pages 1083-1113.

Color Atlas and Textbook of Diagnostic Microbiology, Koneman, 5thedition, Chapter 3, pages 152-153, 162.

Bailey & Scott’sDiagnostic Microbiology, Forbes, 11thedition, Chapter 59, pages 917-926, and Chapter 63, pages 972-984.

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