Intrawound Tobramycin Powder Eradicates Surgical Wound Contamination

Study Design. Therapeutic anti-infective trial in rabbits. Objective. The purpose of the present study was to assess the efficacy of intrawound tobramycin powder in terms of eradicating a known bacterial contamination in an Escherichia coli-infected rabbit spinal implantation model. Summary of Background Data. Implant-associated surgical site infections (SSIs) remain a dreaded complication of spinal surgery. Currently, >30% of all spine SSIs are secondary to gram-negative bacteria. Methods. Twenty healthy New Zealand white female rabbits underwent simulated partial laminectomies and implantation of a 10-mm titanium wire at L5-L6. All surgical sites were inoculated with 100μL of tobramycin-sensitive E coli (EC ATCC 25922, 1×10 6 colony-forming units [CFU]/mL). Before closure, tobramycin powder (120mg) was placed into the wound of 10 rabbits. All rabbits were sacrificed on postoperative day 4. Tissue and wire samples were explanted for bacteriologic analysis. A Fisher exact test was used to assess differences in categorical variables and an independent samples t test was used to assess mean group differences. Results. The experimental and control rabbits were similar in weight (mean±standard deviation, 3.22±0.12kg and 3.22±0.14kg, respectively, P=1.0), sex distribution, and duration of surgery (13.1±2.4minutes and 11.6±2.1minutes, P=0.39). Bacterial cultures of the tissue samples were negative for all 10 tobramycin-treated rabbits and positive for all 10 control rabbits (P<0.0001). Bacterial growth occurred in 39 of 40 samples from control rabbits, but zero of the 40 samples from the tobramycin group (P<0.0001). Blood culture samples from all rabbits were negative for bacterial growth. No rabbit had evidence of sepsis or tobramycin toxicity. Conclusion. In a rabbit spine-infection model, intrawound tobramycin eliminated E coli surgical site contamination. All rabbits without intrawound tobramycin had persistent E coli contamination.