Effect of initial projectile speed on contamination distribution in a lower extremity surrogate "wound track"

This article presents an experimental study that examines the relationship between initial projectile speed and bacterial distribution along a wound track due to surface contamination. A ballistic gelatin cylinder was used as a lower extremity surrogate, and surface contamination was simulated using circular filter paper moistened with a solution containing Escherichia coli strain K-12 that was previously transformed to express green fluorescent protein and be resistant to ampicillin. An 11.43-mm caliber round-nose lead projectile was shot through the contaminated area and into the extremity surrogate at firing velocities ranging from 61 to 199 m/s. The "wound track" was extracted and cut into 10 evenly spaced slices. Then, the permanent cavity was removed from each slice using a biopsy punch, liquefied, and grown on selective agar containing ampicillin. Direct and normalized bacterial colony counts and normalized extents of area covered by bacteria colonies were used to compare the differences between distribution trends corresponding to different projectile speeds. The results obtained showed that, for the cases considered, an increase in projectile speed resulted in a significant shift in the percentage of contamination from the "wound" entrance region to the "wound" exit region.