Activity of florfenicol for Actinobacillus pleuropneumoniae and Pasteurella multocida using standardised versus non-standardised methodology

L Dorey,S Hobson,P Lees

doi:10.1016/j.tvjl.2016.11.004

Abstract

Four indices of antimicrobial potency were determined for florfenicol and the pig pneumonia pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), mutant prevention concentration (MPC) and time–kill curves were determined in two matrices, broth and pig serum. Five overlapping sets of two-fold dilutions were used to increase accuracy of the measurements. MIC and MBC serum:broth ratios for A. pleuropneumoniae were 0.96:1 and 1.07:1, respectively, and corresponding values for P. multocida were 0.72:1 and 0.50:1. The percentage binding of florfenicol to serum protein was 65.4%, and fraction unbound (fu) serum MICs were significantly lower, by 2.71-fold and 3.82-fold, respectively, than predicted for free serum concentrations for A. pleuropneumoniae and P. multocida. Similar culture medium differences were obtained for MBC and MPC. MICs in serum and broth were increased significantly and progressively for high, medium and low initial inoculum counts. Serum MPC:MIC ratios for A. pleuropneumoniae and P. multocida were 12.5:1 and 13.6:1, respectively; ratios for broth were similar. The killing action of florfenicol had the characteristics of concentration dependency for both species in both growth media. These data indicate the value of using a biological medium, when determining microbiological potency indices, to predict dosage for clinical use.

Highlights

Activity of florfenicol for the porcine pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida using standardised versus non-standardised methodology
Florfenicol has been used in pigs for the therapy of pneumonia caused by the microorganisms Actinobacillus pleuropneumoniae, Pasteurella multocida and Bordetella haemolytica (Kehrenberg et al, 2008)
For A. pleuropneumoniae, Minimum inhibitory concentration (MIC) were similar in broth (0.38 μg/mL)

Summary

Introduction

Activity of florfenicol for the porcine pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida using standardised versus non-standardised methodology. Four indices of antimicrobial potency were determined for florfenicol and the pig pneumonia pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), mutant prevention concentration (MPC) and time-kill curves were determined in two matrices, broth and pig serum. MICs were significantly lower, 2.71-fold and 3.82-fold, respectively, than predicted for free serum concentrations for A. pleuropneumoniae and P. multocida. MICs in serum and broth were increased significantly and progressively for high, medium and low initial inoculum counts. The killing action of florfenicol had the characteristics of concentration dependency for both species in both growth media. These data indicate the value of using a biological medium, when determining microbiological potency indices, to predict dosage for clinical use. In vitro studies have demonstrated bactericidal, concentration-dependent activity at concentrations close to the minimum inhibitory concentration (MIC) against some veterinary pathogens (Illambas et al, 2013; Sidhu et al., 2014)

Methods

Results

Discussion

Conclusion