What are the culture results for a pressure (decubitus) ulcer?

From the Guidelines

Decubitus wound cultures are generally not recommended for routine management of pressure ulcers or bedsores, and instead, clinical assessment of signs of infection should guide treatment decisions. When infection is suspected based on signs like increasing pain, erythema, purulent drainage, foul odor, or systemic symptoms, a tissue biopsy or validated quantitative swab technique (Levine method) is preferred over surface swabs 1. The Levine method involves cleansing the wound with normal saline, rotating a swab with pressure over a 1 cm² area until fluid is expressed from the tissue. For infected wounds, empiric antibiotic therapy should target common pathogens including Staphylococcus aureus, Streptococcus species, anaerobes, and gram-negative bacteria. Treatment typically includes amoxicillin-clavulanate 875/125 mg twice daily or, for penicillin-allergic patients, clindamycin 300-450 mg four times daily plus ciprofloxacin 500 mg twice daily for 7-14 days. Cultures help guide therapy when wounds fail to respond to initial treatment or in cases of severe infection. This approach is based on understanding that surface cultures often reflect colonization rather than true infection, while deeper tissue samples better represent the actual infecting organisms.

Some key points to consider when interpreting wound culture results include:

• Sole or predominant bacterial species identified on culture of a good quality specimen are likely true pathogens 1
• Multiple organisms isolated, especially from superficial ulcers, can make it difficult to determine which are pathogens
• Clinical microbiology services must work closely with clinicians and report results in a manner that is easily understood by the recipients
• Targeting antibiotic treatment against likely colonizers may be unnecessary, but these species can sometimes be true pathogens, especially if they grow repeatedly or from reliable specimens

It's also important to note that infections requiring hospitalization are often polymicrobial and may include various types of aerobes and anaerobes, and that multidrug-resistant organisms, especially MRSA, are more often isolated from patients who have recently received antibiotic therapy, who have been previously hospitalized or reside in a chronic care facility or who have had a previous amputation 1.

In terms of the method of obtaining wound cultures, tissue biopsies are considered the gold standard for identifying and differentiating pathogenic organisms from colonizers 1, but are invasive, expensive, and require specialized expertise. Semiquantitative swab cultures using the Levine technique are a safe and inexpensive alternative, but have been shown to be imprecise and do not correlate with quantitative culture results.

Overall, the approach to decubitus wound cultures should prioritize clinical assessment and empiric antibiotic therapy, with cultures used to guide therapy in cases of severe infection or when wounds fail to respond to initial treatment.

From the Research

Decubitus Wound Cultures

• Decubitus wound cultures are not recommended as a routine practice, but rather when there is a clinical suspicion of infection 2, 3.
• The goal of wound cultures is to identify the causative organisms and guide antibiotic therapy 2, 3.
• Tissue biopsy is considered the gold standard for diagnosing infection, but swab culture is the most frequently employed method in clinical settings 2, 3.
• Properly performed swab cultures can provide useful data to augment diagnostic and therapeutic decision making 2, 4.

Techniques for Obtaining Wound Cultures

• There is controversy among practitioners regarding the technique to use for obtaining wound cultures 3.
• The Levine technique, which involves swabbing the wound after debridement or cleaning down to viable tissue, is one method that has been studied 4.
• Wound biopsy and swab cultures can provide similar assessments of wound infection, but there may be variability between individual experts 5.

Interpretation of Culture Results

• Culture results should be interpreted in the context of clinical information and should not be used to determine if a wound is infected, but rather to identify potential pathogens 4.
• The presence of multidrug-resistant organisms (MDROs) in wound cultures should heighten the clinician's level of concern and guide antibiotic therapy 6, 4.
• Institution-specific studies are needed to provide guidelines for choosing effective empirical therapy and preventing infection and its complications in patients with decubitus wounds 6.