Identification of Polysialic Acid and Chondroitin-like Polysaccharides of Moraxella bovis Strains Associated with Infectious Bovine Keratoconjunctivitis

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 α(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 α(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.

Keywords: Moraxella bovis; bacterial capsule; chondroitin; infectious bovine keratoconjunctivitis; polysaccharide structure; polysialic acid.