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Activity of florfenicol for Actinobacillus pleuropneumoniae and Pasteurella multocida using standardised versus
1Hawkshead Campus, Royal Veterinary College, Hatfield, Herts AL97TA, United Kingdom.
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.
Insights
Florfenicol
Area of Science:
- Veterinary Pharmacology
- Antimicrobial Resistance
- Microbiology
Background:
- Florfenicol is a crucial antibiotic for treating bacterial infections in pigs.
- Accurate determination of antimicrobial potency is vital for effective treatment strategies.
- Understanding florfenicol's activity in different biological matrices is essential for optimizing dosage.
Purpose of the Study:
- To evaluate florfenicol's antimicrobial potency against Actinobacillus pleuropneumoniae and Pasteurella multocida.
- To compare antimicrobial indices in broth versus pig serum.
- To assess the impact of protein binding and inoculum size on florfenicol efficacy.
Main Methods:
- Determined minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and mutant prevention concentration (MPC).
- Utilized time-kill curves in both broth and pig serum matrices.
- Investigated the effect of varying inoculum sizes and calculated serum protein binding.
Main Results:
- Florfenicol's potency indices (MIC, MBC, MPC) differed between broth and serum, influenced by protein binding.
- Higher inoculum counts significantly increased MIC values in both media.
- Florfenicol exhibited concentration-dependent killing for both pathogens.
Conclusions:
- Using pig serum as a matrix provides a more biologically relevant assessment of florfenicol's antimicrobial potency.
- These findings support the use of serum-based data for predicting effective florfenicol dosages in clinical settings.
- Understanding matrix effects is critical for accurate antimicrobial potency determination and therapeutic guidance.
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