Distribution of Bacterial Contamination in Partial Penetration Surrogate Ballistic Wounds

Abstract

With the rise in use of IEDs during armed conflicts, there has been an increase in the number of injuries to the extremities. Shrapnel and debris ejected during the explosion become high-speed projectiles capable of penetrating soft tissues, bringing bacterial contamination into the wound. If not properly treated, that contamination could lead to infection. Studies aimed at understanding the distribution of bacterial contamination along the permanent cavity could provide useful information to improve treatment protocols for these types of injuries. In this paper, a lower extremity surrogate model was used to investigate bacterial distribution in partial penetration ballistic wounds. The targets used were ballistic gelatin blocks that had an Escherichia coli-laden filter paper placed on their front face. Spherical projectiles were fired into the targets adjusting their speed to obtain three different partial penetration depths. After each shot, a gelatin strip containing the permanent cavity was extracted and segmented. The permanent cavity was removed from each segment, placed in a test tube with buffer solution, and heated in a water bath to melt the gelatin. Standard microbiology protocols were followed to determine the number of colony forming units (CFUs) in each segment. The bacteria distribution was represented by percent of total CFU in the permanent cavity versus segment number. In addition, bacterial contamination as a function of projectile penetration depth was explored. For the cases considered, most of the bacterial contamination occurred in the segments closer to the projectile entry point.