Effect of Projectile Caliber and Speed on Bacterial Distribution in a Leg Surrogate

This paper examines the relationship between ballistic factors and bacterial distribution along a surrogate wound channel using ballistic gelatin cylinders with dimensions representative of the calf region of an average human leg. The ballistics factors considered were projectile caliber and speed, and Escherichia coli (E. coli) was used as the representative bacteria. In order to reduce the possibility of contamination by outside bacteria, the E. coli first underwent a transformation protocol to express Green Fluorescent Protein (GFP) and become resistant to the antibiotic ampicillin. A set volume of bacteria was pipetted onto a small piece of filter paper which was placed on the surface of a ballistic gelatin cylinder and a projectile was shot through the bacteria saturated filter paper. The ‘wound track’ was divided into slices, and the area surrounding the permanent cavity was removed with a biopsy punch, liquefied, and grown on selective LB media containing ampicillin. Examination of the bacterial colony count along the permanent cavity segments allowed comparison of how variations in projectile caliber and speed affected contamination distribution along the ‘wound track’. Initial results indicate that larger calibers may result in higher contamination distribution at the projectile entrance and exit regions and higher speeds compress the distribution and result in a drop in contamination level near the exit.