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Characterization of nontypeable Actinobacillus pleuropneumoniae isolates

Ho To1,2, Kaho Teshima1,2, Michiha Kon1,2

  • 1Nippon Institute for Biological Science, Ome, Tokyo, Japan (To, Teshima, Kon, Yasuda, Akaike, Shibuya, Nagai, Sasakawa).

Journal of Veterinary Diagnostic Investigation : Official Publication of the American Association of Veterinary Laboratory Diagnosticians, Inc
|June 11, 2020
PubMed

Insights

Transposable elements like IS Apl1 in Actinobacillus pleuropneumoniae can disrupt capsule and O-polysaccharide production. This finding explains why some bacterial isolates appear nontypeable despite testing positive for specific genes.

Area of Science:

  • Veterinary Microbiology
  • Bacterial Genetics
  • Swine Disease Research

Background:

  • Porcine pleuropneumonia, caused by Actinobacillus pleuropneumoniae, is a significant swine respiratory disease.
  • Accurate serotyping is crucial for diagnosing and controlling outbreaks.
  • Some isolates present challenges in traditional typing methods.

Purpose of the Study:

  • To investigate the genetic basis for atypical serotyping results in Actinobacillus pleuropneumoniae isolates.
  • To determine the role of transposable elements in capsule and O-polysaccharide biosynthesis.
  • To understand the implications for bacterial typing and pathogenesis.

Main Methods:

  • Polymerase Chain Reaction (PCR) for capsular serovar 15-specific gene detection.
  • Agar Gel Precipitation (AGP) test for serotyping.
  • Nucleotide sequence analysis of polysaccharide biosynthesis gene clusters.
  • Immunoblot analysis to assess O-polysaccharide production.

Main Results:

  • Two clinical isolates were PCR-positive for serovar 15 but AGP-negative (nontypeable).
  • Sequence analysis revealed the presence of the transposable element IS Apl1 in polysaccharide biosynthesis gene clusters of both isolates.
  • Immunoblotting confirmed the absence of O-polysaccharide production in these isolates.
  • The IS Apl1 element was implicated in the disruption of both capsular polysaccharide (CPS) and lipopolysaccharide O-polysaccharide (O-PS) biosynthesis.

Conclusions:

  • The transposable element IS Apl1 of Actinobacillus pleuropneumoniae can interfere with the biosynthesis of both CPS and O-PS.
  • This interference can lead to nontypeable isolates despite the presence of specific serotype genes.
  • Understanding these genetic mechanisms is vital for accurate diagnostics and effective disease management in swine.
Keywords:
Actinobacillus pleuropneumoniaeinsertion sequence ISApl1nontypeableswine

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