Purpose: The uptake of (99m)Tc-UBI (29-41) was evaluated at sites of bacterial infections in rabbits before and after treatment with ciprofloxacin.
Methods: Staphylococcus aureus susceptible to ciprofloxacin was used to induce a focal infection in each rabbit of group 1 (G1), group 2 (G2), and group 3 (G3) with 2 x 10(4), 2 x 10(6), and 2 x 10(8) colony forming units (CFU), respectively. After 24 h, images of infected thighs (target: T) and contralateral thighs (nontarget: NT) were acquired. Animals then received ciprofloxacin intramuscularly for 5 days followed by imaging on the third and fifth days. The control group 4 (G4) was imaged at days 1, 3, and 5 under the same acquisition parameters. Group 5 (G5) was employed to study biodistribution of the peptide.
Results: Increases in (T/NT) ratios in G1, G2, and G3 were observed from 5 min onwards with maximum values at 60 min. G3 revealed the highest accumulation of the peptide. Growth of the same strain of S. aureus on blood agar medium was visualized after fine needle aspiration. After ciprofloxacin treatment, the images for G1-G3 resulted in significantly decreased (P < 0.05) T/NT values on the third and fifth days that correlated with reduction in number of viable bacteria. No significant difference (P < 0.05) in left to right thigh ratios in the control group (G4) was observed. Biodistribution of the peptide showed rapid removal of tracer from circulation through the kidneys.
Conclusions: ( 99m ) Tc-UBI (29-41) accumulation directly correlates with the number of viable bacteria. This infection localization agent can be utilized for monitoring efficacy and duration of antibiotic treatment.