Studies on the pathogenesis of avian pathogenic E. coli (APEC) infections and development of new combat strategies against Colisepticaemia in poultry.

 

Avian pathogenic E. coli (APEC) are responsible for the well known colisepticaemic infections in the poultry industry, resulting in large economic losses. Most prevalent is a systemic infection which inevitably results in inflammatory changes of internal organs and tissues (e.g. Air sac infection, inflammation of the heart and oviduct).
Despite intensive in-depth research, and knowledge of numerous virulence-associated factors, the pathogenic mechanisms of APEC, particularly their entry into the blood stream remains uncertain. There is a lack of successful combat strategies, as would be the case with a vaccine, and often, anti inflammatory substances arrive too late due to the rapid progress of infection. Our research focuses on the molecular typing of an extensive culture collection and the development of molecular diagnostic procedures and methods, in order to identify pathogenic E. coli of avian origin (Multiplex-PCR for APEC Diagnostics). A combination of virulence-gene typing and Phylogenetic analysis would enable a global interpretation about the origin and distribution of clonal APEC groups as well as the identification of a reservoir of avian pathogenic E. coli strains unknown to date.

An important project in our group towards pathogenesis research with regards to the development of disease in poultry is the application of Signature-tagged transposon mutagenesis (STM) to in vivo infection assays with adult SPF chickens. With the help of two newly established Infection models (“Septicaemia” and “Lung infection model”), a large number of STM-generated mutants were tested for their attenuation in vivo. In the septicaemia model, over 30 APEC virulence genes were identified that appeared to play a crucial role in the infection process of avian colibacillosis. Currently, 1.800 new STM mutants are being tested in a Lung infection model, in order to identify adhesion-associated genes that play a significant role in the initial stages of APEC infection, particularly the colonization of the respiratory epithelium (DFG Graduiertenkolleg [GRAKO]).

Virulence attenuated mutants, as also gene loci and their gene products identified in this manner are further characterized in vitro with the help of adhesion and invasion assays. For this purpose we specifically use chicken macrophages and chicken fibroblast cell lines.

In the framework of the FUGATO (Funktionelle GenomAnalyse im Tierischen Organismus) project funded by the Federal Ministry of Education and Research (BMBF), in cooperation with immunologists and animal breeders, the established chicken infection models form the basis for further studies particularly host-pathogen interactions during APEC infection. In this networked project, the individual partners would evaluate the molecular virulence of APEC, the innate and acquired immunity and the genetic resistance of the host. The aim of this work is to compile all research data for new breeding strategies, so that these in turn may practically be put to use in poultry breeding. This could further enable an integrated and combined approach for the development of vaccines.
IVIAT (In Vivo Induced Antigen Technology), a method which allows identification of genes in the respective host during a natural or experimental infection, also forms part of the FUGATO project.

All projects eventually lead to a better understanding of colisepticaemia pathogenesis among poultry, as well as host-pathogen interactions during an APEC infection. These are the basic requirements for the successful development of an efficient vaccine. In reality, the establishment of an effective immunising procedure would be adjudged to be of great importance, because prophylactic and therapeutic measures for combating APEC infection are limited due to acute infection, waiting period, and spread of multiresistance against anti-infective substances.

Due to the lack of knowledge about pathogenically relevant antigens, currently available commercial vaccines provide insufficient protection, which in exceptional cases, can provide an alternative to coop- and type-specific vaccines only for certain companies, and is therefore not future oriented.

An important aspect of our work is therefore, to test genes identified by different methods (STM, IVIAT) as potential vaccine candidates. Extensive information, technologies at our disposal, together with virulence typing, Phylogenetic analysis, and in vitro and in vivo assays, form the basis for the selection of prototype strains that would eventually play a role in vaccine development in the future.

 

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