Autotransporters belong to a group of virulence factors secreted by Gram-negative bacteria using a simple mechanism termed type V or autotransporter secretion. These large proteins have diverse virulence functions, and many are found to play relevant roles in bacterial infections. An autotransporter polypeptide is equipped with two translocator domains (signal peptide and ß -domain), which enable its own export across bacterial membranes. Because of significant sequence conservation in the translocator domains among various species, genes of putative autotransporters can be easily identified in bacterial genomic sequences. Thereafter, gene expression can be determined and protein localization elucidated. Such a method for identifying autotransporter virulence proteins may be an important first step in understanding bacterial pathogenicity or discovering new targets for antimicrobial and vaccine development.