Antibiotic sensitivity of an Argentine strain collection of Moraxella bovis

The antimicrobial susceptibility of 88 isolates of Moraxella bovis of Argentine origin was evaluated for 12 antimicrobials by broth microdilution procedures. The isolates had a minimum inhibitory concentration (MIC90) of < or = 0.06 microg/mL to enrofloxacin; < or = 0.12 microg/mL to ceftiofur; < or = 0.25 microg/mL to ampicillin; < or = 0.5 microg/mL to florfenicol and gentamicin; < or = 1.0 microg/mL to tilmicosin, erythromycin, and oxytetracycline; < or = 4.0 microg/mL to tylosin; < or = 8.0 microg/mL to spectinomycin; < or = 0.25/4.75 microg/mL to trimethoprim/sulfamethoxazole; and > or = 32 microg/mL to lincomycin. Modal MIC values for these antimicrobials were as follows: enrofloxacin, 0.03 microg/mL; ceftiofur, 0.06 pg/mL; ampicillin, 0.25 microg/mL; florfenicol, gentamicin, erythromycin, and oxytetracycline, 0.5 microg/mL; tilmicosin, 1.0 microg/mL; tylosin and spectinomycin, 4.0 microg/mL; lincomycin and erythromycin, 16 microg/mL; and trimethoprim/ sulfamethoxazole, < or = 0.25/4.75 microg/mL. These data show that all antimicrobials except lincomycin have MICs suggestive of sensitivity in vitro, though confirmation of clinical efficacy can only be properly assessed based on pharmacologic and/or clinical data to support the MIC values.