Influence of Projectile Momentum and Kinetic Energy on Bacterial Distribution in an Extremity Surrogate “Wound Track”

This paper presents an experimental study that examines the relationship between the initial momentum and the initial kinetic energy of a projectile and the distribution of bacterial contamination along a “wound track” created in an extremity surrogate representative of the superior (upper) portion of the lower leg (i.e., the calf region) of an average adult human male. Initial surface contamination was represented using circular filter paper moistened with a solution containing 5 × 10⁶ colony forming units per milliliter (CFU/ml) of Escherichia coli strain K-12 that was previously transformed to express green fluorescent protein (GFP) and be resistant to ampicillin. The contaminated filter paper and extremity surrogate were perforated with 11.43-mm (0.45-in) caliber round nose lead projectiles shot from commercially available air rifles. To match the initial momentum and/or kinetic energy between experiments, 11.0 g (170 grain) and 14.9 g (230 grain) projectiles were shot at velocities ranging from 145 m/s to 195 m/s. The “wound track” was extracted from the extremity surrogate and sliced into small, evenly spaced segments and the permanent cavity was removed from each segment using a biopsy punch, liquefied, and grown on selective agar containing ampicillin. Examination of the bacterial colony count and area covered by bacteria colonies per segment allowed comparison of differences between trends in the bacteria distribution along the “wound track”. The results obtained showed that, for the cases considered, the bacterial distribution trends were similar for the experimental groups with like initial kinetic energies.