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Plasmid-encoded NAD independence in some South African isolates of Haemophilus paragallinarum

R R Bragg1, L Coetzee, J A Verschoor

  • 1Department of Poultry Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.

The Onderstepoort Journal of Veterinary Research
|June 1, 1993
PubMed

Insights

Atypical Haemophilus paragallinarum strains causing infectious coryza in South African poultry no longer require V factor (NAD) for growth. Plasmid transfer demonstrated that this NAD independence is plasmid-borne.

Area of Science:

  • Veterinary Microbiology
  • Poultry Diseases
  • Bacterial Genetics

Background:

  • Infectious coryza is a significant respiratory disease in poultry.
  • Haemophilus paragallinarum is the primary causative agent.
  • Atypical strains with altered growth requirements are emerging.

Purpose of the Study:

  • To characterize atypical Haemophilus paragallinarum isolates from South African poultry.
  • To investigate the genetic basis of V factor (NAD) independence in these strains.

Main Methods:

  • Isolation and re-inoculation of bacteria into specific-pathogen-free (SPF) chickens.
  • Serological typing using monoclonal antibodies and enzyme-linked immunosorbent assay (ELISA).
  • Plasmid extraction and conjugation experiments to assess genetic transfer.

Main Results:

  • Atypical H. paragallinarum isolates were recovered from infected chickens.
  • Some isolates were serologically related to serotype A, while others showed no reaction.
  • All atypical isolates were NAD-independent, unlike typical strains.
  • Plasmid transfer conferred NAD independence to reference strains.

Conclusions:

  • Atypical H. paragallinarum strains are circulating in South African poultry.
  • NAD independence in these strains is a plasmid-mediated trait.
  • This finding has implications for understanding bacterial adaptation and disease control.

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