If a culture from a wound was sent to the lab for work up, explain the steps you would take to isolate and identify the causative agent. (Include...

Common Pathogens Found in Wounds

Staph. aureus, Beta hemolytic Strep. (S. pyogenes, S. agalactiae), E. coli, Proteus, Klebsiella, Pseudomonas, Acinetobacter, Stenotrophomonas, anaerobic bacteria

Wound Infection Progress and Gram Test Results

Particular types of bacteria may be suspected based on the age of the wound and the gram test results.

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  Early Acute Wound: Normal skin flora, followed by Staph. Aureus and Beta-hemolytic Strep.; mostly gram positive bacteria


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  About Four Weeks: facultative anaerobic gram negative rods such as Proteus, E. coli, and Klebsiella


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  Longer Term Wound: Anaerobic bacteria become more common


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  Long Term Chronic Wound: Often contain more anaerobic bacteria than aerobic bacteria - aerobic gram negative rods also seen; Examples include Pseudomonas, Acinetobacter, Stenotrophomonas

Common Culture Media

The following culture media can be used to isolate specific types of organisms:

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  Mannitol Salt Agar: Use to isolate Staphylococci and Micrococci


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  Phenylethyl Alcohol Agar: Use to isolate gram positive bacteria


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  Blood Agar: Use to grow most bacteria


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  Chocolate Agar: Used to isolate Neisseria and Haemophilus 

Common Enzymatic Tests

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  Catalase: Positive - Staphylococci; Negative - Streptococci and most anaerobes


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  Coagulase: Positive - Staphylococcus aureus


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  Oxidase: Positive - most gram negative bacteria

*Please also see the first reference listed below, which shows a detailed flowchart for the identification of bacteria based on differential culture media, enzymatic tests, and resistance patterns.