A number of enterobacterial outer membrane proteins which are involved in virulence and seem to promote the invasion of bacteria into eukaryotic cells have been shown [1,2] to be structurally related. These proteins are listed below.

• Escherichia coli and Enterobacter cloacae outer membrane protein X (gene ompX).
• Salmonella typhimurium virulence membrane protein pagC.
• Yersinia enterocolitica attachment invasion locus protein (gene ail).
• Bacteriophage lambda outer membrane protein lom. Lom is expressed during lysogeny in Escherichia coli.

These outer membrane proteins have from 150 to 170 amino acid residues and their sequences are well conserved. We selected the two most highly conserved regions as signature patterns. The first pattern is located in the N-terminal section of these proteins; the second is located at the C-terminal extremity.