In ballistic injuries, contamination can be carried from the environment, clothing, and skin surface into the wound track. Bacteria and contaminated debris can be introduced into the wound by several means, including physical transport by the projectile or by the suction caused by the formation and collapse of the temporary wound cavity. In this paper, the relationship between initial bacterial concentration on the surface and resultant bacterial distribution along the wound channel is examined using a leg surrogate. Escherichia coli strain K-12 was used to represent skin surface contamination. In order to reduce the possibility of contamination by outside bacteria and assist in colony visualization, the E. coli first underwent a transformation protocol to express Green Fluorescent Protein and to be resistant to the antibiotic ampicillin. Different concentrations of bacteria were pipetted onto circular filter paper and placed onto the surface of a ballistic gelatin leg surrogate, and an 11.43-mm (0.45-in) caliber projectile was shot through the contaminated area into the gel. The “wound track” was sliced into small, evenly spaced samples and the permanent cavity was removed using a biopsy punch, liquefied, and grown on selective lysogeny broth media containing ampicillin. Examination of a normalized bacterial colony count and normalized area covered per segment allowed comparison of variations in the initial concentration, and confirmed that within a range the normalized contamination distribution trend along the “wound track” remained similar. This verification allowed additional confidence in results obtained using this bacteria distribution methodology by eliminating concerns over small variations in initial bacterial concentration.

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