Tracing the origin of bacterial contamination in close and medium range gunshot wounds in a sheep limb model

Abstract

Background: Gunshot injuries have a variable rate of infection, the source of remains debatable. This study aimed to determine whether bacteria found on bullets, within the gun barrel or on the victim’s skin and clothing could be deposited into the deep tissues and bone at the time of injury. And to determine the effects of bullet design, soft tissue thickness and victim distance on bacterial deposition. Methods: Fifty-two sheep legs were shot in the tibia or femur at close range (10cm) or medium range (5m) with .22mm rifles, using solid or hollow point bullets. Streptomycin resistant Streptococcus salivarius was inoculated along different points of the bullet path including the bullet, barrel, skin and clothing. Results: Bacteria were isolated in the deep tissues and bone in all samples with varying consistency. Interestingly, the hollow point bullet deposited bacteria more consistently than the solid point, bacteria within the barrel were transmitted to the target even at 5m and no observable difference was seen in the rate of bacterial transmission between tibial and femoral gunshot wounds. Conclusions: We confirm previous research, showing that low velocity bullets do not auto-sterilise on firing. In addition, we show that bacteria can be deposited into the deep tissues in a viable state, irrespective of soft tissue thickness. Importantly, hollow point bullets transmit bacteria more consistently than pointed tip bullets, and finally, bacteria anywhere along the bullet’s path can be collected by the bullet and deposited into the deep tissues in close and medium range experimental gunshot wounds.