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Bacterial Balance in Healing Chronic Pressure Ulcers

Am Fam Physician. 2000 May 1;61(9):2852.

Chronic wounds, such as pressure ulcers, can be frustrating to treat. Systemic antibiotics do not reach therapeutic levels in chronic granulation tissue and do not appear to influence levels of bacterial growth. Water-based topical antibacterial creams penetrate the depths of such wounds and can directly affect bacterial colonization. The basis of successful wound treatment appears to be adequate removal of all debris and devitalized tissue. Sharp debridement remains the basis of therapy, and irrigation an important adjunct, especially in intermittent treatment. Enzymatic debridement tends to allow bacterial proliferation.

High levels of bacteria not only result in infection but also inhibit normal wound healing. Levels of bacteria above 105 per g of tissue produce proteases and other products that interfere with the healing processes and may lead to invasive infection. Beta-hemolytic streptococci are particularly virulent because they produce multiple enzymes and other products that enhance bacterial spread. Once a wound is obtained, healing depends on the ability to maintain bacterial balance. Robson and colleagues conducted a study to evaluate whether a chronic wound, once in bacterial balance, can maintain that balance.

They obtained weekly biopsies from patients participating in a blinded, placebo-controlled, cytokine clinical trial. During the screening period, all patients underwent debridement. The appropriate water-based antibacterial cream was applied to the wound twice daily. Participants underwent biopsies until bacterial balance was achieved. At that time, topical antibacterial creams were discontinued for a seven-day washout period until participants had completed screening, randomization was completed, and an initial biopsy was obtained. Qualitative and quantitative bacterial analyses were performed on a weekly basis for the 35-day treatment period. Each patient underwent six biopsies. Of the 363 cultures, 350 (96 percent) showed a bacteria count of less than 102 per g of tissue. Only four specimens (1 percent) showed a count of greater than 105 per g of tissue at any time during the trial.

The authors conclude that in the absence of beta-hemolytic streptococci with a bacteria count of no more than 105 per g of tissue, wounds can maintain bacterial balance once it is established. They stress that once adequate debridement has occurred, the granulating tissue is remarkably resistant to invasive infection. Chronic wounds, such as pressure ulcers, can sustain bacterial balance and resist infection if well cared for and kept free of necrotic avascular tissue.

Robson MC, et al. Maintenance of wound bacterial balance. Am J Surg. November 1999;178:399–402.


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