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In vitro susceptibility of porcine respiratory pathogens to tilmicosin
D C DeRosa1, M F Veenhuizen, D J Bade
1Elanco Animal Health, Greenfield, IN 46140, USA.
Abstract:
Bacterial isolates obtained from swine with various clinical diseases were tested for susceptibility to tilmicosin by minimum inhibitory concentration (MIC) and Kirby-Bauer disk diffusion tests using National Committee on Clinical Laboratory Standards methodology. The tilmicosin MIC90 was < or =0.125 microg/ml for Erysiopelothrix rhusiopathiae, < or = 1 microg/ml for Haemophilus parasuis isolates, 8 microg/ml for Actinobacillus suis and Pasteurella multocida type A, 16 microg/ml for toxigenic and nontoxigenic P. multocida type D, 64 microg/ml for Bordetella bronchiseptica, and >128 microg/ml for Staphylococcus hyicus and Streptococcus suis. The results of disk diffusion testing matched well with the MIC results for each pathogen. This in vitro survey of tilmicosin activity against various swine isolates suggests that further clinical evaluation of tilmicosin in swine may be warranted for disease associated with E. rhusiopathiae, H. parasuis, and A. suis but not B. bronchiseptica, S. suis, or S. hyicus.
Insights
Tilmicosin shows promising in vitro activity against key swine pathogens like Erysipelothrix rhusiopathiae and Haemophilus parasuis. Further clinical studies are recommended for these bacteria, but not for Bordetella bronchiseptica or Streptococcus suis.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Susceptibility Testing
- Swine Infectious Diseases
Background:
- Tilmicosin is a macrolide antibiotic used in veterinary medicine.
- Swine bacterial diseases pose significant economic challenges in animal agriculture.
- Understanding tilmicosin's efficacy against prevalent swine pathogens is crucial for treatment strategies.
Purpose of the Study:
- To evaluate the in vitro susceptibility of various swine bacterial isolates to tilmicosin.
- To determine the minimum inhibitory concentration (MIC) and disk diffusion profiles for tilmicosin against common swine pathogens.
- To identify bacterial species for which tilmicosin warrants further clinical investigation in swine.
Main Methods:
- Bacterial isolates from diseased swine were tested.
- Minimum Inhibitory Concentration (MIC) and Kirby-Bauer disk diffusion assays were performed.
- National Committee on Clinical Laboratory Standards (NCCLS) guidelines were followed.
Main Results:
- Tilmicosin demonstrated high in vitro activity (MIC90 ≤ 1 µg/ml) against Erysipelothrix rhusiopathiae and Haemophilus parasuis.
- Moderate activity was observed against Actinobacillus suis and Pasteurella multocida (MIC90 = 8-16 µg/ml).
- Low activity was noted against Bordetella bronchiseptica, Staphylococcus hyicus, and Streptococcus suis (MIC90 ≥ 64 µg/ml).
Conclusions:
- Tilmicosin exhibits potent in vitro efficacy against E. rhusiopathiae, H. parasuis, and A. suis.
- Clinical evaluation of tilmicosin is warranted for swine diseases caused by these three pathogens.
- Tilmicosin is unlikely to be effective against B. bronchiseptica, S. hyicus, and S. suis based on these in vitro results.