Intrawound Tobramycin Powder Eradicates Surgical Wound Contamination: An In Vivo Rabbit Study.

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 100 μL of tobramycin-sensitive E coli (EC ATCC 25922, 1 × 10 colony-forming units [CFU]/mL). Before closure, tobramycin powder (120 mg) 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 ± 0.12 kg and 3.22 ± 0.14 kg, respectively, P = 1.0), sex distribution, and duration of surgery (13.1 ± 2.4 minutes and 11.6 ± 2.1 minutes, 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.

LEVEL OF EVIDENCE: N /A.