Use of a Commercial Broth Microdilution Technique for Testing the Susceptibility of Haemophilus Somnus to Antimicrobials

Abstract

H. somnus has been recognized as an important opportunistic pathogen associated with bovine morbidity worldwide. While data are available on the antimicrobial susceptibility of H. somnus these have been generated using the agar dilution (6,7) or disc diffusion (1) techniques. A broth medium is available for the testing of some Haemophilus species (4) although it has not been recommended for testing H. somnus. The broth microdilution technique offers advantages of economy, convenience and reproducibility over more traditional methods of susceptibility testing (3). In particular, the Sensititre® system, using commercially prepared antimicrobial plates with extended room temperature storage, is well suited to veterinary diagnostic laboratories. The objective of this study was to adapt the Sensititre broth microdilution technique for determination of the antimicrobial susceptibility of H. somnus field isolates.