Cath Lab Digest

Dear Editor,

Regarding the article, “The 10⁵ Bacterial Growth Guideline: Reassessing its Clinical Relevance in Wound Healing” (Ostomy/Wound Management. 2003;49[1]:44–53), the interrelationships among micro-organisms and host resistance are well-known and accepted, and the author correctly notes the need to understand these relationships in comprehending the complexities of soft tissue infections. However, his perusal of selected articles on quantitative bacteriology and its usefulness leaves the reader with several injudicious conclusions.

The two major monographs on bacterial balance^1,2 contain the same discussions presented by Bowler, including sections on virulence, pathogenicity, host defense mechanisms, and antimicrobials. The main differences between those monographs and the Bowler article are the inclusion of hard data.

It is a biological fact that a balance or equilibrium exists between bacteria and host resistance factors, and when equilibrium is upset in favor of the bacteria, potential for infection occurs. In all of the studies reviewed since the turn of the 20^th century, the balance fulcrum is at approximately 1 million organisms per gram of tissue or mL of biologic fluid. The numerical distribution, like all biologic phenomena, forms a bell-shaped curve. Therefore, some infections might be expected to occur with fewer numbers of bacteria, and occasionally, no infection will be present when large numbers of bacteria are noted.

All of the data published suggest that 10⁵ or fewer bacteria per gram of tissue are compatible with normal wound healing. Bowler explains how quantitative bacterial analyses are performed and, therefore, realizes that >10⁵ means beyond that exact tube dilution or at least 1 x 10⁶.

The real problem with the article is the suggestion that the bacterial balance concept using a numerical bacterial burden is not clinically relevant. In the original study performed on wound closure by skin grafts, 94% of grafts were successful when wounds contained 10⁵ or fewer bacteria per gram of tissue; while only 19% were successful when 10⁵ bacteria per gram were present.³ This is clinically relevant. In the next study⁴ of wound approximations, 28 out of 30 wounds were successfully closed when the wounds contained 10⁵ or fewer bacteria; whereas, 0 out of 10 wounds were successfully closed when >10⁵ organisms/gram were present, which is clinically relevant. Specialists dealing with acute and chronic wounds have reported similar data. In one monograph,² the data are referenced for chronic wounds, general surgery, orthopedic surgery, plastic surgery, thoracic surgery, and burns. In each case, the usefulness of the numerical concept of evaluating the bacterial equilibrium is validated as to clinical relevance. Bowler suggests that surgeons may find these principles more useful because their views might differ from those of a microbiologist. All of the studies on quantitative bacteriology from our laboratories included a microbiologist (John P. Heggers, PhD). In fact, Dr. Heggers is the senior author of the above-mentioned monograph.

Bowler specifically states that the venous stasis ulcer is a polymicrobial-contaminated wound and questions the value of quantitative bacteriology. Two recent articles may be of interest. In a review of data from a clinical trial of repifermin (KGF-2), Falanga⁵ showed that the number of bacteria at the time of initial screening affected the response to growth factors (ulcers with less than 1 x 10⁶ bacteria per gram of tissue at screening fared better). Similarly, Sibbald,⁶ reporting on the treatment of chronic wounds with cell-based therapies, found that wounds not in bacterial balance did not respond as well.