A concentration gradient of bacteria within wound tissues and scab.

This investigation was designed to evaluate the effect of a synthetic moisture vapor permeable dressing on the size of the bacterial population of superficial wounds. Split-thickness donor sites were created in pig skin and were treated with a synthetic occlusive dressing (Tegaderm), with fine mesh gauze, or with nothing. All wounds became spontaneously infected with a variety of bacteria, predominantly with Staphylococcus epidermidis. The population of the Tegaderm wounds was always greater than that of the untreated controls, while that of the gauze treated wounds was equal to or less than that of the controls. Tegaderm dressed wounds healed more quickly than did the others. A gradient in the concentration of bacteria within the wounds was seen, with a very high concentration in the scab (10(8) cells/g), an intermediate concentration (10(6) cells/g) in the dermal layer, and the lowest concentration (10(4) cells/g) in the hypodermal level of the wound tissue. Such a gradient has not previously been reported. No evidence was seen that the level of infection declined over time for any of the dressings. Apparent bacterial clearing in earlier investigations may be due to the progressive loss of superficial wound tissues with the corresponding exclusion of the high concentration of bacteria within these layers from the tissue sampled.