Post-antibiotic effect of marbofloxacin, enrofloxacin and amoxicillin against selected respiratory pathogens of pigs

The post-antibiotic effect is defined as the period of bacterial growth suppression that persists after a limited exposure of organisms to antimicrobials and knowledge of its duration is important in establishing and optimising current dosing schedules for the treatment of bacterial infections. The post-antibiotic effect of marbofloxacin, enrofloxacin and amoxicillin were evaluated in vitro for Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida strains which originated from clinical samples of diseased pigs and were confirmed as susceptible to all tested antimicrobials based on determination of minimal inhibitory concentrations. The post-antibiotic effect for individual antimicrobials was monitored at five and ten times minimum inhibitory concentrations for one and two hours. The duration of the post-antibiotic effect for tested antimicrobials was found to exhibit the following order for all tested pathogens: marbofloxacin > enrofloxacin > amoxicillin. The longest duration of post-antibiotic effect of all tested antimicrobials was found in A. pleuropneumoniae and the shortest post-antibiotic effect duration was detected in P. multocida. No statistical differences in post-antibiotic effect duration were found within marbofloxacin and enrofloxacin in A. pleuropneumoniae and H. parasuis strains. In P. multocida strains there was a statistically significant difference (P = 0.0189). On the other hand, the differences between amoxicillin and marbofloxacin or enrofloxacin were statistically significant in all cases (P-values ranged between 0.0058 and 0.008). The prolonged post-antibiotic effect of fluoroquinolones and amoxicillin on important Gram-negative swine pathogens was confirmed. The results can be used to clarify the effect and mechanism of action of antimicrobial drugs in veterinary medicine.