aro mutants of Salmonella enterica are frequently used as live vaccines for the oral vaccination of domestic animals. Interestingly, besides their auxotrophy, they appear to be of reduced resistance to the components of innate immune response due to a defect in outer membrane and/or cell wall integrity. Because different extracellular structures associated with the cell wall or outer membrane are involved in biofilm formation, we were interested in the ability of aroA and aroD mutants of S. Enteritidis to adhere to solid surfaces. We found that aroA and aroD mutants did not adhere to solid surfaces although they bind Congo red and produced D-mannose and D-glucose capsular polysaccharides in the same amounts as the wild-type strain. However, the aro mutants exhibited a decreased production of cellulose, N-acetyl-D-glucosamine or N-acetylneuraminic acid containing capsular polysaccharide and fimbriae which explains their inability to form biofilms. aroA and aroD containing plasmids complemented all the defects of the aro mutants. Beside its attenuation for different hosts, the loss of ability to form biofilm is an additional interesting characteristic of aro mutants.