In vitro susceptibility of porcine respiratory pathogens to tilmicosin

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 Clin ical Laboratory Standards methodology. The tilmicosin MIC90 was <0.125 mug/ ml for Erysiopelothrix rhusiopathiae, less than or equal to1 mug/ml for Hae mophilus parasuis isolates, 8 mug/ml for Actinobacillus suis and Pasteurell a multocida type A, 16 mug/ml for toxigenic and nontoxigenic P. multocida t ype D, 64 mug/ml for Bordetella bronchiseptica, and >128 mug/ml for Staphyl ococcus hyicus and Streptococcus suis. The results of disk diffusion testin g matched well with the MIC results for each pathogen. This in vitro survey of tilmicosin activity against various swine isolates suggests that furthe r clinical evaluation of tilmicosin in swine may be warranted for disease a ssociated with E. rhusiopathiae, H. parasuis, and A. suis but not B. bronch iseptica, S. suis, or S. hyicus.