It is well established that virulence factors are often located on mobile elements, such as plasmids or pathogenicity islands and are thus often subjected to horizontal gene transfer . Sequence analyses of aatA and check details the flanking regions revealed a potential of mobility for the adhesin gene. In all completely sequenced E. coli genomes, where an aatA sequence was detected, the gene locus was enclosed by transposable elements. Furthermore, episomally located aatA variants might be transferred in the context of the whole plasmid,
presuming the presence of functional transfer and mobility elements. In addition, possible sequence variations among aatA genes of strains allocated to different phylogenetic groups might be reflected functionally, which has for example been shown for the genes of the fim cluster . Since aatA was retained in isolates of different phylogenetic groups, the discrete function of the protein in the respective strains, whether they commensally colonize the intestine or invade other internal organs of poultry and cause severe systemic CCI-779 cost infections, remains unsolved to date and should be subjected to thorough investigations in
the future. Many autotransporter adhesins are known to be relevant not only for adhesion but also for biofilm formation, invasion, aggregation and toxicity . Adhesins related to AatA, such as Hap, Ag43, AIDA and TibA, for example, contribute Methocarbamol to bacterial aggregation by intercellular passenger domain interactions . Most trimeric autotransporter adhesins also seem to confer serum resistance by binding to components of the complement system . Although IMT5155 does not produce a biofilm under normal lab conditions, it remains to be determined if in vivo conditions might probably trigger this phenotype, enabling to investigate a possible role of AatA in this process. Although Li et al. suggested that AatA is not involved in autoaggregation or biofilm formation , it did not become evident whether they tested the wild-type and mutant strain, observing no difference,
or whether the wild-type strain APEC_O1, comparable to IMT5155, did not show these phenotypes in general. Conclusion A chromosomal variant of the autotransporter adhesin gene aatA, which has recently been described in the plasmid pAPEC-O1-ColBM of APEC_O1  was identified in APEC strain IMT5155. The gene product conferred adhesion of a fim-negative K-12 strain to DF-1 cells and its passenger domain was able to trigger immune responses in rabbits. Prevalence studies clearly hinted towards a special importance of this adhesin in avian pathogenic E. coli strains, whether outbreak or so-called reservoir strains, while an essential functional role for other animal and human ExPEC strains cannot be inferred from the present data.