Chapter 8: Assessing and Controlling Bioburden

Introduction

Acute wound healing has been described to occur in the overlapping cascade of events of inflammation, proliferation, and remodeling. These events are presumed to occur whether the wound is an acute surgical wound closed by primary intention or an open traumatic wound left to close by secondary intention through contraction, granulation, and epithelialization. The timing of these events will vary depending on a variety of factors including, but not limited to, the duration of wounding; the location, size, and depth of the wound; the causative factors; the presence of comorbid conditions that can delay healing; the patient's age; and certainly the presence of bacteria in numbers great enough to interfere with normal cellular events.¹

Human skin can be considered the boundary between the human organism and the outside environment, providing an effective barrier to bacterial contamination and invasion into deeper tissues. By its very nature, the skin provides its own defense.

The dry, dead, keratinized cells on the surface prevent most microorganisms from infiltrating into deeper layers. In addition, cells from the stratum corneum are shed every day, and attached microorganisms slough off with them.² The normal pH range of the skin is 4 to 6.5.^3,4 The production of sebum from the sebaceous glands contributes to this low pH, making the skin a more hostile environment for microbial growth. Sebum is also high in lipids, which could serve as a nutrient to bacteria, but the fatty acid breakdown of the lipids produces toxic by-products that inhibit the growth of potentially pathogenic bacteria. Sweat, because of its low pH and high salt concentration, is also inhibitory to microorganisms.² Additionally, small populations of resident bacteria such as Staphylococcus epidermidis and skin diphtheroids help prevent colonization by more pathogenic bacteria such as Staphylococcus aureus.⁵ A breach of this boundary, or break in the skin, allows access for both pathogenic as well as normal residential skin flora to penetrate deeper tissues, which provide the warmth, moisture, decreased oxygen, and nutrients bacteria require to thrive and multiply.

The role of bacteria located in and on an open wound has been the subject of numerous citations in the literature over the past decades. Practitioners must understand the role that bacteria play in wound healing and nonhealing, appropriately assess and make clinical judgments based on the known or presumed level and host impact of any bacterial presence, and make treatment decisions based on the sum of all of this information.

Bioburden, according to the University of Rochester glossary, is the number of microorganisms with which an object is contaminated.⁶ According to Stedman's Medical Dictionary the term bioburden is defined as the degree of microbial contamination or microbial load; the number of microorganisms contaminating an object.⁷ By ...