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Exopolysaccharide Production and Biofilm Formation by Histophilus somni

Briana Petruzzi1, Thomas J Inzana2

  • 1Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061, USA.

Current Topics in Microbiology and Immunology
|February 9, 2016
PubMed

Insights

Histophilus somni biofilms differ between pathogenic and commensal strains, with pathogenic strains producing more exopolysaccharide (EPS). A new diagnostic test detects EPS antibodies, distinguishing systemic disease from colonization.

Area of Science:

  • Veterinary Microbiology
  • Bacterial Pathogenesis
  • Host-Pathogen Interactions

Background:

  • Histophilus somni forms complex biofilms with structural variations between pathogenic and commensal isolates.
  • Exopolysaccharide (EPS) is a major biofilm component, with higher production observed in pathogenic H. somni.
  • The EPS composition is a D-mannan polymer, similar to yeast mannan, and can be modified by sialic acid.

Purpose of the Study:

  • To characterize the structural differences in Histophilus somni biofilms between pathogenic and commensal isolates.
  • To investigate the composition and properties of the H. somni biofilm matrix.
  • To evaluate a novel diagnostic test for distinguishing systemic H. somni disease from colonization.

Main Methods:

  • Comparative analysis of biofilm architecture and EPS production in pathogenic and commensal H. somni isolates.
  • Biochemical characterization of EPS composition, including the effects of sialic acid.
  • In vitro biofilm formation assays following a standard growth curve.
  • In vivo demonstration of H. somni biofilm formation in experimentally challenged animals.
  • Serological analysis using a diagnostic test detecting antibodies to EPS.

Main Results:

  • Pathogenic H. somni isolates produce significantly more biofilm and EPS than commensal isolates.
  • The H. somni EPS is a D-mannan polymer, with sialylation occurring in the presence of sialic acid, yielding N-acetylglucosamine and N-acetylgalactosamine.
  • H. somni biofilms were confirmed in cardiopulmonary tissue, often co-occurring with Pasteurella multocida.
  • A diagnostic test detecting anti-EPS antibodies accurately identifies animals with systemic H. somni disease.

Conclusions:

  • Biofilm structure and EPS production are key differentiators between pathogenic and commensal Histophilus somni.
  • The composition of the H. somni EPS can be influenced by host-derived molecules like sialic acid.
  • A novel diagnostic approach targeting EPS antibodies shows promise for clinical differentiation of H. somni infections.

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