Analysis of immune responses induced by avian pathogenic Escherichia coli infection in turkeys and their association with resistance to homologous re-challenge

Jean-Rémy Sadeyen,Mark P Stevens,Francis Dziva,Pete Kaiser

doi:10.1186/1297-9716-45-19

Abstract

Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease in poultry yet the nature and consequences of host immune responses to infection are poorly understood. Here, we describe a turkey sub-acute respiratory challenge model and cytokine, cell-mediated and humoral responses associated with protection against homologous re-challenge. Intra-airsac inoculation of turkeys with 105 colony-forming units of APEC O78:H9 strain χ7122nalR induced transient and mild clinical signs of colibacillosis followed by clearance of the bacteria from the lungs and visceral organs. Upon re-challenge with 107 χ7122nalR, primed birds were solidly protected against clinical signs and exhibited negligible bacterial loads in visceral organs, whereas age-matched control birds exhibited high lesion scores and bacterial loads in the organs. Levels of mRNA for signature cytokines suggested induction of a Th1 response in the lung, whereas a distinct anti-inflammatory cytokine profile was detected in the liver. Proliferative responses of splenocytes to either Concanavalin A or soluble χ7122nalR antigens were negligible prior to clearance of bacteria, but APEC-specific responses were significantly elevated at later time intervals and at re-challenge relative to control birds. Primary infection also induced significantly elevated χ7122nalR-specific serum IgY and bile IgA responses which were bactericidal against χ7122nalR and an isogenic Δrfb mutant. Bactericidal activity was observed in the presence of immune, but not heat-inactivated immune serum, indicating that the antibodies can fix complement and are not directed solely at the lipopolysaccharide O-antigen. Such data inform the rational design of strategies to control a recalcitrant endemic disease of poultry.

Highlights

Avian pathogenic Escherichia coli (APEC) are a leading cause of morbidity and mortality in poultry and exert significant economic and welfare costs
Development of a turkey model of sub-acute primary APEC O78:H9 infection Intra-airsac inoculation of two-week-old turkey poults with 105 colonyforming units (CFU) of APEC O78:H9 strain χ7122nalR resulted in mild clinical signs which resolved within 24 h in all the challenged birds
Five birds were randomly sampled per group to determine the level of bacterial colonisation, the degree of pathology and the induction of splenocyte responses

Summary

Introduction

Avian pathogenic Escherichia coli (APEC) are a leading cause of morbidity and mortality in poultry and exert significant economic and welfare costs. Respiratory viral or Mycoplasma infections, the onset of sexual maturity and stress associated with sub-optimal husbandry practices are leading antecedents to colibacillosis in farmed poultry. Despite improvements in poultry production systems over the years, APEC continue to pose a formidable challenge to poultry farmers, threatening food security at a time of increasing global demand. The expansion of free-range production systems in Europe and elsewhere may be expected to increase the incidence of colibacillosis owing to greater exposure of farmed birds to environmental pathogens, stress and injury associated with formation of a social hierarchy. In field surveys colibacillosis was the most common bacterial infection in birds reared free-range (with cases peaking between onset of lay and 30 weeks of age) and a positive correlation between vent-pecking and the incidence of colibacillosis was reported [5,6]

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Conclusion