Veterinary and Biomedical Sciences, Department of


First Advisor

John Dustin Loy

Date of this Version

Fall 11-23-2021


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Integrative Biomedical Sciences, Under the Supervision of Professor John Dustin Loy. Lincoln, Nebraska: December, 2021

Copyright © 2021 Matthew Michael Hille


Infectious bovine keratoconjunctivitis (IBK) represents the most common ocular disease of cattle. Moraxella bovis (M. bovis) is the only bacteria proven to cause IBK under experimental conditions. A closely related bacteria, Moraxella bovoculi (M. bovoculi) is cultured from IBK lesions more frequently than M. bovis, and is suspected to cause IBK, although a causal relationship between M. bovoculi and IBK has not been confirmed experimentally. Two distinct genotypes were recently characterized in M. bovoculi based on whole genome sequencing. Genotype 1 M. bovoculi appears to represent a potential pathogen whereas genotype 2 M. bovoculi appears to represent a nonpathogenic normal flora of the ocular and oropharyngeal surface based on frequencies of isolation from IBK outbreaks and normal animals. We demonstrated that M. bovoculi isolates can be accurately classified according to genotype using a novel matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) biomarker model. Some genotype 1 strains of M. bovoculi possess operons encoding for a repeats-in-toxin (RTX) exotoxin that is a known virulence factor for a number of veterinary pathogens. A separate MALDI-TOF MS biomarker model was developed that accurately characterized M. bovoculi isolates according to the presence or absence of the RTX exotoxin. Together, these biomarker models can be used to screen for isolates that are genotype 1 and RTX + which are more likely to represent potential pathogens. To assess the efficacy of two different IBK vaccine formulations, we performed a 5-year randomized clinical control trial in a cow/calf herd in eastern Nebraska. Vaccine treatments included a commercially available M. bovis vaccine, as well as an autogenous vaccine that incorporated antigens from M. bovis, M. bovoculi, and Mycoplasma bovoculi. The incidence of IBK in both treatment groups did not differ from that of a negative control vaccine group. Additionally, when we examined the humoral immune response of vaccinated calves to a known M. bovis virulence factor, the relative levels of specific antibodies did not correlate to disease status.

Advisor: John Dustin Loy