Identification of polysialic acid and chondroitin-like polysaccharides of Moraxella bovis strains associated with infectious bovine keratoconjunctivitis

Authors: VIONNET, JUSTINE - Food And Drug Administration(FDA); PETERSON, DWIGHT - Food And Drug Administration(FDA); LOY, JOHN - University Of Nebraska; WYNN, EMILY - Orise Fellow; BATTISTEL, MARCOS - Food And Drug Administration(FDA); HILLE, MATTHEW - University Of Nebraska; Clawson, Michael; VANN, WILLIE - Food And Drug Administration(FDA)

Submitted to: ACS Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2025
Publication Date: 12/4/2025
Citation: Vionnet, J., Peterson, D.C., Loy, J.D., Wynn, E., Battistel, M., Hille, M., Clawson, M.L., Vann, W.F. 2026. Identification of polysialic acid and chondroitin-like polysaccharides of Moraxella bovis strains associated with infectious bovine keratoconjunctivitis. ACS Infectious Diseases. 12(1):152-161. https://doi.org/10.1021/acsinfecdis.5c00628.
DOI: https://doi.org/10.1021/acsinfecdis.5c00628

Interpretive Summary: Infectious bovine keratoconjunctivitis (IBK), also known as pinkeye, is the most common ocular disease of cattle and costs the U.S. beef and dairy industries over 100 million dollars annually. IBK is caused by the bacteria pathogen Moraxella bovis, and efficacious vaccines for M. bovis are needed to prevent the disease. M. bovis produce capsules, which are special outer layers that encase and protect the bacteria from immune clearance by the host, but sometimes capsule components can be used to generate efficacious vaccines. In this study, the major capsule components of multiple M. bovis strains were identified. The majority of M. bovis strains had capsules comprised of a chrondroitin-like molecule. One outlier strain had a capsule comprised of a polysialic acid. Both of these capsules mimic sugar chains found on the cells of cows. These discoveries enhance understanding of how M. bovis may cause IBK and may provide targets for vaccines to protect cattle from this disease.

Technical Abstract: Moraxella bovis is a major etiologic agent for infectious bovine keratoconjunctivitis (IBK), commonly known as bovine pink eye. IBK has been a major economic burden to the cattle and dairy industries due to its economic and welfare impacts on affected cattle herds. Antimicrobial treatment of acute IBK infections is often challenging. Vaccine formulations widely used in industry have poor efficacy for the prevention of IBK. Capsular polysaccharides of some bacterial pathogens are important epidemiological markers and are successfully used in vaccines for humans. Currently, there are limited data demonstrating the presence of capsular polysaccharides in M. bovis. In this study, we show by genomic analysis that a broad selection of M. bovis strains obtained from the eyes of cattle harbor a gene cluster for expressing capsular polysaccharides. The isolates potentially express either a chondroitin-like polysaccharide or an a(2-8) polysialic acid. We isolated a polysaccharide from cultures of a well-studied model strain for IBK, the Epp63 strain, structurally identical to capsule a(2-8) polysialic acid of the human pathogens Escherichia coli K1 and Neisseria meningitidis Group B. The gene cluster in M. bovis Epp63 encodes a polysialyltransferase similar to other bacterial polysialyltransferases. Other M. bovis strains analyzed in this study possess a gene homologous to that of bacterial chondroitin synthase. We isolated a capsular polysaccharide from M. bovis genotypes 1 and 2 that has the repeat unit identical to nonsulfated chondroitin. These findings provide a tool for the study of M. bovis IBK pathogenesis that could lead to approaches for better control of the disease.