Veterinary and Biomedical Sciences, Department of


Date of this Version



Journal of Veterinary Diagnostic Investigation 26:6 (2014), pp. 761– 768.

doi: 10.1177/1040638714551403


Copyright © 2014 John Dustin Loy and Brad W. Broderson. Published by SAGE. Open access licensed.


Infectious bovine keratoconjunctivitis (IBK), also known as pinkeye, is the most costly eye disease of cattle. The principal etiologic agent of IBK is the Gram-negative bacterium Moraxella bovis. However, there have been reports of IBK outbreaks associated with Moraxella bovoculi. A retrospective study of IBK diagnostic cases submitted from July 1, 2010, through October 31, 2013, was conducted. Included in the study were 1,042 Moraxella isolates from 1,538 swabs of lacrimal secretions collected from 282 herds from 30 U.S. states. Moraxella isolates were identified to the species level and were composed of M. bovoculi (701 isolates), M. bovis (295 isolates), Moraxella ovis (5 isolates), and other Moraxella spp. (41). Minimum inhibitory concentrations required for 90% growth inhibition (MIC90) was calculated for representative isolates. The MIC90 values for both M. bovis and M. bovoculi were as follows: ampicillin and ceftiofur: ≤ 0.25 μg/ml; clindamycin: 2 μg/ml; danofloxacin and enrofloxacin: ≤ 0.12 μg/ml; florfenicol: 0.5 μg/ml; gentamicin: 1 μg/ml; neomycin: 4 μg/ml; tulathromycin: 2 μg/ml; and tylosin: 8 μg/ml. The MIC90 values for M. bovoculi included the following: chlortetracycline: ≤ 0.5 μg/ml; oxytetracycline: 4 μg/ml; penicillin: 0.25 μg/ml; spectinomycin: 32 μg/ml; sulfadimethoxine: > 256 μg/ml; tiamulin: 1 μg/ml; and trimethoprim-sulfamethoxazole: 4 μg/ml. For M. bovis, MIC90 values included the following: chlortetracycline and oxytetracycline: 1 μg/ml; penicillin: ≤ 0.12 μg/ml; spectinomycin: 16 μg/ml; sulfadimethoxine: ≤ 256 μg/ml; tiamulin: ≤ 0.5 μg/ml; and trimethoprim-sulfamethoxazole: ≤ 2 μg/ml. The current work describes the frequency of isolation and differences in antimicrobial sensitivity observed among Moraxella isolates from case submissions.