Minimal inhibitory and Mutant prevention concentrations of enrofloxacin for Pasteurella multocida from rabbits affected by pasteurellosis

Pasteurella multocida is the agent of one of the most significant diseases in rabbits and it is associated with a heterogeneous clinical picture. Drugs belonging to the fluoroquinolones class are useful to control pasteurellosis. Among them, enrofloxacin is one of the most used molecules in rabbit industry and it is the only one fluoroquinolone registered for this species in Italy. Enrofloxacin adopted dosages are currently based on Minimum Inhibitory Concentration (MIC). Nevertheless, MIC is not effective against possible pathogen sub-populations with lower susceptibility that may be selectively amplified, leading to possible problems of antibiotic resistance. Mutant Prevention Concentration (MPC) could represent an approach to minimize the risk of resistance selection in pathogens. The aim of this work was to test the sensitivity to enrofloxacin of P. multocida strains isolated from rabbits affected by pasteurellosis to evaluate if MPC-based dosages can represent a valid option. The study was performed on ten strains of P. multocida isolated from rabbits from two industrial farms of Puglia, South Italy. The sensitivity to enrofloxacin has been evaluated by MIC tests by microdilution method and MPC tests performed according to Marcusson et al. (2005) with minor modifications. The results of MIC and MPC tests have revealed that MPC dosages are on average 8,4 times higher than MIC dosages. This data highlight that, although MPC-based dosages are useful to prevent the selection of potential mutant, they could be higher than MIC-based ones, leading to possible issues related to their application in field, for example the potential risk of possible toxicity for animals and residues in meat.