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

TL;DR

This study identifies polysaccharides in Moraxella bovis, a bacteria causing bovine pink eye, which could help develop better vaccines and treatments.

Contribution

The study reveals that M. bovis strains produce either polysialic acid or chondroitin-like polysaccharides, offering new insights for disease control.

Findings

M. bovis strains possess gene clusters for producing capsular polysaccharides like polysialic acid or chondroitin.

A polysaccharide isolated from M. bovis Epp63 is structurally identical to human pathogen polysialic acid.

Polysaccharides from genotypes 1 and 2 match nonsulfated chondroitin in structure.

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.

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