Effects of Comparative Killing by Pradofloxacin and Seven Other Antimicrobials Against Varying Bacterial Densities of Swine Isolates of Pasteurella multocida

Bacterial killing is important for recovering from infection. Pasteurella multocida is a key bacterial pathogen causing swine respiratory disease and is associated with substantial mortality. Antimicrobial therapy remains an important therapeutic intervention for treating infected animals. Pradofloxacin (fluoroquinolone) is the most recently approved antimicrobial agent for treating pigs with swine respiratory disease. We compared in vitro killing of swine P. multocida strains by pradofloxacin in comparison to ceftiofur, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin, and tulathromycin over a range of bacterial densities and four clinically relevant drug concentrations. Pradofloxacin killed 92–96.9% of cells across 106–108 cfu/mL densities at the mutant prevention drug concentration following 2–24 h of drug exposure, 96.9–98.9% of cells across 106–109 cfu/mL at the maximum serum drug concentration following 30 min of drug exposure, increasing to 99.9–100% kill following 12–24 h of drug exposure. At the maximum tissue drug concentration and against bacterial densities of 106–109 cfu/mL, pradofloxacin killed 91.3–99.8% of cells following 2 h of drug exposure, which increased to 99.9–100% kill following 12–24 h of drug exposure. Pradofloxacin was rapidly bactericidal across a range of bacterial densities and at clinically relevant drug concentrations. Pradofloxacin will be an important antibiotic for treating pigs with swine respiratory disease and where clinically indicated.